Question 101·Medium·Text Structure and Purpose
Biologist Dr. Malik was puzzled that a marsh once bustling with frogs had become nearly silent. Surveys revealed that though adult frogs were present, very few tadpoles survived. After heavy spring rains, agricultural runoff poured into the marsh, coating eggs with silt that blocked oxygen exchange. To verify the cause, Malik incubated eggs in clean water and in water mixed with runoff; only the latter showed high mortality.
Which choice best describes the function of the underlined portion in the text as a whole?
For function questions in Reading & Writing, first restate the underlined sentence in your own words, then look at the sentence right before and right after to see how it fits into the mini-story (introducing a problem, proposing a cause, giving evidence, stating a result, etc.). Decide its role (for example, hypothesis vs. result vs. background) before checking the choices, then cross out any option that adds details not in the passage (like trends or contrasts that aren’t mentioned) or misplaces where in the logic (before/after the experiment) the sentence appears.
Hints
Zoom in on the underlined sentence
Ignore the answer choices at first. Reread only the underlined sentence and put it into your own words: what event is it describing, and what effect does that event have on the frog eggs?
Look at the sentences before and after
Ask: what problem is introduced before the underlined sentence, and what does Malik do after it? Does the underlined sentence come before or after the experiment and its results?
Think about the type of information it adds
Is the underlined portion telling you numbers or trends, describing an experimental result, setting up a possible cause, or comparing two different types of threats?
Eliminate choices that don’t match the passage
Check each answer against the passage: Does the passage actually talk about a decline in adult frogs? Does the underlined part actually give experimental results or a contrast between two categories of threats?
Step-by-step Explanation
Understand what the underlined sentence literally says
Reread the underlined portion: heavy spring rains cause agricultural runoff to pour into the marsh, which coats frog eggs with silt and blocks oxygen exchange. In simple terms, it’s describing how runoff might interfere with the eggs getting enough oxygen.
See how it connects to the rest of the passage
Before the underlined sentence, we are told that very few tadpoles survive. After the underlined sentence, Malik runs an experiment incubating eggs in clean water vs. runoff water to verify the cause. This means the underlined sentence is not the result of the experiment; it is the idea about what might be causing the mortality that he then tests.
Match that role to the best answer choice
We have determined the underlined sentence proposes what might be killing the tadpoles (runoff coating eggs and blocking oxygen), which is an attempted cause for their low survival that Malik later tests. That matches choice B) It suggests a potential explanation for the low survival rate of tadpoles in the marsh.