Question 120·Hard·Text Structure and Purpose
Algal blooms are frequently attributed to fertilizer runoff from farms, and policy responses have largely targeted agricultural practices. Yet limnologist Mara Chen’s decade-long survey of three watersheds showed that bloom frequency did not meaningfully decline despite documented reductions in farm nutrient inputs; substantial decreases occurred only after upgrades at urban wastewater treatment plants reduced phosphorus from combined sewer overflows. Chen argues that undercounted urban sources have been the dominant driver, cautioning that efforts focused exclusively on agriculture risk misallocating resources.
Which choice best describes the main purpose of the text?
For main-purpose questions, summarize in one sentence what the author is mainly doing (for example, “using new data to question a common belief”). Then eliminate choices that (a) focus on a minor detail (like methods), (b) shift the scope (like treating two causes as equally emphasized), or (c) add claims the passage doesn’t make. The best answer will match the passage’s overall movement from setup to evidence to conclusion, especially as signaled in the first and last sentences.
Hints
Focus on the beginning and end
Reread the first and last sentences. What commonly held view is mentioned at the start, and how does Chen’s conclusion at the end respond to that view?
Ask what the study results are used for
Are the study findings mainly used to describe how the research was done, to show there are many equal causes, or to support a particular shift in how people think about the problem?
Eliminate purposes the passage doesn’t clearly support
Check each answer and ask: Does the passage actually spend time arguing for funding, laying out detailed methods, or giving separate solutions, or is it doing something more focused with its evidence?
Step-by-step Explanation
Identify the topic and claim
Read the first and last sentences to see the big picture.
- First sentence: Algal blooms are “frequently attributed” to farm fertilizer runoff, and policy has targeted agriculture.
- Last sentence: Chen argues urban sources have been the “dominant driver” and warns that focusing only on agriculture risks misallocating resources.
So the passage contrasts a common belief and existing policies with Chen’s different conclusion and warning.
Notice how the evidence is used
Look at the middle of the passage to see what Chen’s study actually shows.
- Farm nutrient inputs went down, but bloom frequency did not meaningfully decline.
- Bloom frequency dropped only after upgrades at urban wastewater plants reduced phosphorus.
This pattern of results is used to challenge the initial, widespread attribution to farms and to highlight the importance of urban wastewater sources.
Clarify what the passage is not mainly doing
Before choosing an answer, check what the passage does not focus on:
- It does not go into detailed methods or discuss limitations of the survey.
- It does not treat agricultural and urban sources as equally responsible.
- It does not focus mainly on praising a specific intervention; it uses that intervention as evidence for a broader policy point.
Its central move is to use study results to challenge the usual explanation and to warn that policy attention is aimed in the wrong place.
Match the overall purpose to the answer choices
Compare your summary to the choices. The passage’s main purpose is to use Chen’s decade-long data to question the standard blame placed on agricultural runoff and to suggest that policy focus should shift toward undercounted urban wastewater sources.
Therefore, the best choice is: To present evidence that challenges a common attribution of algal blooms and redirects policy attention.