Pronoun Reference and Main Idea in a Coral Passage
An OAT passage begins: 'When seawater warms even one degree Celsius above the summer maximum, corals expel the algae living in their tissues. This stress turns the colony stark white - a condition called bleaching. Reefs can recover if temperatures fall within weeks, but repeated events exhaust them. Scientists therefore monitor degree-heating weeks, a cumulative measure of thermal pressure. They caution that this metric says nothing about local pollution or fishing pressure, which can compound the damage.' A student must answer: 'The word They in the last sentence refers to…' Options are (A) corals, (B) repeated events, (C) scientists, (D) degree-heating weeks. The same student also faces a main-idea question and is torn between 'Corals bleach when stressed' and 'Bleaching is measurable but not the whole story of reef decline.'
1. Resolve the referent of 'They' and explain the checks that rule out the other options.
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C, scientists. Three checks converge. Grammar: 'They' is the subject of 'caution,' a verb of speech or judgment that ordinarily takes people as agents; corals and events do not caution. Proximity and number: 'scientists' is the nearest plural noun capable of performing the verb, while 'degree-heating weeks' is the object of 'monitor' and is singular in sense. Discourse: the previous sentence says scientists monitor the metric, so the next sentence naturally continues with what those same scientists warn. Substituting each candidate into the sentence is the fastest filter: only 'scientists caution that…' reads as ordinary English.
2. Which main-idea candidate is stronger, and why does the weaker one fail?
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'Bleaching is measurable but not the whole story of reef decline.' The first candidate is true but functions as background: it covers the opening sentence and stops. The passage's second half - the cumulative metric, then the warning that the metric omits pollution and fishing pressure - is where the author spends structural energy, signaled by 'therefore' and 'but.' Main-idea answers must cover the whole passage, including its qualifications. A reliable test is to ask what the passage would lose if each half were deleted: remove the opening and the caveat still stands; remove the caveat and the passage becomes a definition rather than an argument.
3. What can the student infer about a reef with many degree-heating weeks but little local pollution?
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It faces cumulative thermal stress, so recovery depends on how quickly temperatures fall and how often events recur - the passage says repeated events 'exhaust' reefs. The student can also infer that this reef's dominant risk is heat rather than pollution, because the caveat names pollution and fishing as compounding factors. What cannot be inferred is a specific outcome such as certain death: the passage says reefs 'can recover if temperatures fall within weeks,' so outcome is duration-dependent. Keep the inference to what the text licenses, and treat any answer that predicts a definite result as an overreach.