IELTS Reading 練習問題 — Set 7

A A lake bottom appears uniform from above, but its sediment can preserve a layered record of environmental change. Mineral particles wash in from slopes, microscopic organisms settle after death, and wind carries pollen from surrounding vegetation. In quiet deep water these materials accumulate with limited disturbance. Scientists recover them by lowering a hollow corer into the bed and extracting a cylinder of mud. The newest layer lies near the top; deeper material is generally older, although that simple order must be tested rather than assumed.

B Establishing age is central. Recent layers can sometimes be dated using known pollution markers or radioactive isotopes associated with industrial activity. Older material may contain leaves or charcoal suitable for radiocarbon dating. A core rarely receives a date for every centimetre. Researchers build an age–depth model between measured points, incorporating uncertainty and possible changes in accumulation rate. Floods may deposit a thick layer in hours, while a century of slow deposition elsewhere produces only a thin band.

C Pollen is among the best-known indicators. Its resistant outer wall survives in sediment, and differences in shape allow many plant groups to be identified. Counts reveal shifts from forest to grassland or the arrival of cultivated crops. They do not provide a straightforward map of nearby vegetation. Some species release far more pollen than others, grains travel different distances, and lake size influences the area represented. Analysts use modern calibration data to correct, imperfectly, for these biases.

D Diatoms—algae with silica shells—offer evidence about water conditions. Different species tolerate particular ranges of acidity, salinity and nutrients. When nutrient-loving forms increase, researchers may infer enrichment from soil erosion, sewage or fertiliser. The organisms indicate that conditions changed, not which source caused the change. Historical land records, chemistry and evidence from neighbouring lakes are needed to distinguish competing explanations.

E Charcoal fragments are used to reconstruct fire history, but scale again matters. Fine particles can travel far through the atmosphere, whereas large fragments usually indicate burning nearer the shore. An increase may reflect more fires, larger fires or improved preservation. Human land clearance and climatic drought can produce similar signals. Rather than treating charcoal as a direct fire counter, researchers examine particle size, accumulation rate and correspondence with vegetation change.

F The archive is not always orderly. Burrowing animals mix sediment; underwater currents move particles; methane bubbles disrupt layers. Cores taken near a river mouth may contain dramatic flood records but also erosion gaps. Scientists commonly collect several cores from different parts of a lake. A pattern repeated across locations is less likely to result from a local disturbance, while disagreement can itself reveal how sediment moves within the basin.

G Lake records become especially valuable when combined with written history. Tax documents may date agricultural expansion, maps show drainage works, and diaries describe exceptional winters. Documentary sources are selective and concentrated in recent centuries, while sediment extends farther back but is less precise about individual events. Agreement strengthens interpretation; disagreement forces researchers to reconsider the dating, the proxy or the historical record rather than automatically privileging one.

H Chemical contamination can provide additional chronological markers. Lead from fuel, mercury from industry and artificial radionuclides may rise at historically documented times. Yet pollutants are not always fixed after burial: some dissolve and migrate through pore water, blurring the layer in which they first arrived. Before using a chemical peak as a date, researchers test whether the element is likely to move under the lake’s oxygen and acidity conditions.

I Comparisons between lakes demand similar caution. A regional drought may lower water levels everywhere, but its sedimentary expression depends on basin shape, catchment vegetation and human water use. One core can provide a detailed local history; a network can reveal which changes were shared. Standard protocols help comparison, though rigid uniformity may prevent teams from adapting sampling to very different lakes.

J A core is therefore not a ready-made timeline but a material argument assembled from multiple proxies. Each indicator responds to several processes, and each dating method contains error. The strength of palaeoenvironmental reconstruction lies in convergence: independent traces pointing toward the same change. Its honesty lies in preserving alternatives where convergence is incomplete. Mud can greatly extend environmental memory, but only if the uncertainty between layer and history remains visible.

A Noise is commonly measured in decibels, a scale that describes sound pressure. The number is indispensable but incomplete. Two environments with the same average level can feel entirely different: one may contain a steady ventilation hum, the other intermittent aircraft. Human response depends on pitch, duration, predictability, meaning and perceived control. The study of soundscapes therefore asks not only how much acoustic energy is present but how a place is heard and interpreted.

B Averages hide timing. A road may be moderately loud all day, while a railway creates brief peaks separated by long quiet periods. Energy-based indices can combine these patterns into the same value, though sleep and concentration may respond differently. Analysts supplement averages with maximum levels, event counts and the proportion of time above a threshold. Each measure answers a different question, and selecting one can subtly define what counts as a problem.

C Frequency matters because the ear is not equally sensitive across the spectrum. Standard weightings adjust instruments to approximate human hearing, but low-frequency sound can remain troublesome even when the weighted figure is modest. It travels through walls, produces vibration and may be felt as much as heard. Complaints about turbines or machinery sometimes conflict with official measurements because the metric discounts precisely the component residents notice.

D Meaning also changes reaction. The sound of children in a playground may be welcomed by one listener and judged intrusive by another. Natural sounds such as water and birds can reduce the perceived disturbance of traffic without lowering its measured level. This does not mean pleasant sound simply cancels harmful exposure; rather, context influences appraisal. Soundscape designers sometimes add valued sounds, but they must avoid using decoration to excuse an unnecessarily noisy source.

E Control is another strong predictor of annoyance. Office workers tolerate conversations differently when they can move to a quiet room. Residents may accept occasional festival noise if they were consulted about timing, yet resent a lower level imposed unpredictably. Because control is partly social, an acoustic survey alone cannot capture it. Interviews and diaries reveal when people were disturbed, what activity was interrupted and whether they felt able to respond.

F Seeking “quiet” creates its own measurement difficulty. Extremely low sound is uncommon in cities, and total silence is not necessarily desirable or safe. People use auditory information to judge whether a street is active, whether a vehicle approaches and whether others are nearby. A successful quiet area may contain intelligible, appropriate sounds at low intensity rather than an absence of sound. Researchers increasingly describe acoustic quality instead of pursuing the smallest possible number.

G Equity complicates policy. Wealthier households may purchase insulation or move away from busy corridors, while renters and shift workers have fewer options. Citywide averages can conceal intense exposure in particular neighbourhoods and at particular hours. Monitoring networks have also been distributed unevenly, with more sensors where complaints are already organised. Participatory mapping can reveal neglected areas, though self-reported data must be interpreted alongside physical measurements.

H Long-term health evidence often relies on exposure models that combine traffic, building form and limited monitoring. Personal devices offer finer time patterns but may alter behaviour and are expensive to deploy widely. Stationary sensors support continuous records yet cannot follow an individual between home, work and transport. Studies increasingly combine both, accepting that better coverage and better personal detail pull sampling design in different directions.

I Ecological sound adds another outcome. Noise can mask animal calls, change feeding behaviour and divide habitat even where human annoyance is low. Weightings based on the human ear are inappropriate for species that hear other frequencies. An assessment framed around public comfort may therefore miss biological effects. Declaring the intended listener—human or otherwise—is part of declaring what a sound metric means.

J No single indicator can therefore rank every sound environment fairly. A transparent assessment states which outcome matters—hearing damage, sleep, communication, comfort or ecological disturbance—and selects measures accordingly. It also records the experiences that numbers miss. Quantification remains essential for standards and enforcement, but precision should not be confused with completeness. Measuring quiet is ultimately an exercise in making several forms of evidence answerable to one another.

A The familiar image of expertise is an individual who has accumulated unusual knowledge through long study. Modern achievements complicate that image. No single person understands every layer of a commercial aircraft, a climate model or a vaccine supply chain. Reliable performance emerges from networks of specialists, instruments, standards and organisations. Expertise has not disappeared from individuals; it has become dependent on arrangements that allow partial knowledge to be combined.

B This dependence explains why a team of brilliant members can still fail. Information must reach the person able to interpret it, uncertainty must be communicated without being stripped away, and responsibility must remain clear when tasks cross boundaries. In tightly coupled systems, a small misunderstanding can travel quickly. Checklists and standard terminology reduce ambiguity, but excessive standardisation can prevent workers from reporting an unexpected condition that does not fit a category.

C Transactive memory is the shared knowledge of who knows what. Long-standing teams do not all memorise the same facts; members learn where expertise resides and how to access it. This reduces duplication and speeds problem solving. It also creates vulnerability when a key person leaves or when status discourages junior staff from contacting a senior expert. Directories can record formal qualifications, but practical knowledge about whom to trust often remains informal.

D Diversity of expertise can improve judgement because different disciplines notice different risks. An engineer, a nurse and a procurement officer may interpret the same equipment failure through design, patient safety and supply continuity. Diversity is not automatically productive. Without a common language, disagreement may be mistaken for incompetence. Effective boundary roles translate concepts while preserving differences that matter, rather than forcing every discipline into one vocabulary.

E Institutions frequently assess expertise through credentials and publication records because these are visible and comparable. Such indicators are useful filters but imperfect measures of contribution. A technician who maintains an instrument may understand its drift better than a distant author with a prestigious title. Collective expertise requires channels through which operational knowledge can challenge formal authority. Otherwise organisations possess relevant knowledge without allowing it to influence decisions.

F Digital collaboration expands the possible network. Specialists can review images or data across continents, and searchable archives retain solutions to rare problems. Yet remote access removes contextual cues: a photograph may omit the smell, vibration or sequence that alerted someone on site. Platforms also encourage easily documented contributions, while quiet coordination disappears from the record. The archive can therefore distort future judgments about whose work mattered.

G Accountability appears difficult when knowledge is distributed. After failure, investigators may search for one person who should have known. Sometimes negligence is individual, but often each participant acted reasonably within a narrow view while the system failed to connect those views. This does not mean that nobody is responsible. Organisations are responsible for designing escalation routes, protecting dissent and testing whether warnings travel across interfaces.

H Training for collective expertise must include coordination, not just deeper specialisation. Simulations can require participants to locate an unfamiliar expert, challenge a doubtful instruction and hand over an unresolved problem. Assessment then considers whether the network noticed and combined information, rather than whether one person supplied the final answer. Such exercises expose missing relationships that an organisation chart, with its neat boxes and reporting lines, tends to conceal.

I Temporary networks face particular difficulties. Emergency teams, international research collaborations and construction projects bring together people who have not developed shared memory. They compensate with liaison roles, explicit handover formats and preliminary exercises. These devices accelerate trust but cannot manufacture it completely. Time spent learning how another group uses evidence may look inefficient at the start, yet prevents far larger coordination costs later.

J Collective expertise should not be confused with voting on technical truth. Evidence does not become stronger merely because more people endorse it. The collective element concerns the production, checking and application of knowledge. A mature system knows when to broaden participation, when to defer to specialised skill and how to revise that allocation as conditions change. Its achievement is not the elimination of dependence but the disciplined management of it.