Question 59·Medium·Text Structure and Purpose
Many engineers consider large-scale desalination too expensive for remote communities because the process typically relies on costly polymer membranes. Yet in a small coastal town in Chile, engineers have demonstrated a solar-powered desalination system that uses no membranes at all. Built largely from locally sourced clay and recycled glass, the prototype produced enough drinking water for 400 residents during its six-month trial.
Which choice best describes the function of the underlined sentence in the text as a whole?
For “function of a sentence” questions, first read a few lines before and after the sentence to see how the ideas connect. Pay close attention to transition words like “yet,” “however,” “for example,” or “therefore,” since they signal whether the sentence is contrasting, giving an example, explaining, or concluding. Then summarize in your own words what the sentence is doing (e.g., giving a counterexample, defining a term, explaining a cause) and choose the option that best matches that role, eliminating answers that describe functions you simply don’t see in the text (like definitions, procedures, or predictions that aren’t actually there).
Hints
Look at the sentence before the underlined part
What belief or limitation is described in the first sentence, and what is the reason given for it?
Pay attention to the transition word
The underlined sentence begins with “Yet.” How does that word usually connect one idea to the one before it—does it continue, explain, or contrast?
Ask what kind of information the underlined sentence adds
Is the underlined sentence giving a definition, a detailed procedure, a prediction, or a real-life example? How do you know from its wording?
Match the sentence’s role to the answer choices
Once you decide whether the sentence supports, explains, or challenges the previous idea, choose the option that best describes that relationship.
Step-by-step Explanation
Understand the first sentence
Read the first sentence: “Many engineers consider large-scale desalination too expensive for remote communities because the process typically relies on costly polymer membranes.”
This sets up a problem or limitation: desalination is seen as too expensive for remote communities since it depends on expensive membranes.
Examine the underlined sentence and transition word
Look closely at the underlined sentence and especially its first word: “Yet in a small coastal town in Chile, engineers have demonstrated a solar-powered desalination system that uses no membranes at all.”
The word “Yet” signals a contrast with what came just before. The sentence describes a system that:
- Is solar-powered, and
- Uses no membranes at all.
This clearly contrasts with the earlier idea that desalination is expensive because it relies on costly membranes.
Connect the example to the overall point
Notice that the underlined sentence is about one specific case: a small coastal town in Chile where engineers have built a particular system. It is not a general definition or a prediction; it is a concrete example.
Also, what happens in this example shows that desalination can be done without the expensive membranes mentioned earlier. That means it challenges or goes against the limitation described in the first sentence.
Eliminate answer choices that don't match the sentence's role
Now evaluate each option based on how the underlined sentence actually functions:
- It does not list step-by-step methods or say it will be explained later, so it does not outline a procedure.
- It does not define any technical term.
- It does not discuss long-term policy changes or effects.
Instead, it presents a specific contrasting example that shows the earlier limitation is not always true. Therefore, the correct answer is: D) It provides a specific example that contradicts the limitation described in the previous sentence.