Why does the author include the examples of trains, elevators and a surgeon in the fifth paragraph?
Read an Informational Passage · ELPAC Grades 9–10 reading. The correct answer, and the reasoning behind it.
A longer factual text, with questions about the main idea, supporting details and vocabulary.
Read the passage. Then answer the questions.
A Few Seconds of Warning
No one can predict an earthquake. Scientists cannot say that a large one will strike next month, or even next year. What they can do, it turns out, is notice an earthquake that has already begun and warn people before the strongest shaking reaches them. The warning lasts seconds, not minutes, but a surprising amount can happen in a few seconds.
The idea depends on a difference between two kinds of waves. When a fault slips, it sends out a fast, mild wave called a P wave and a slower, stronger wave called an S wave. The P wave moves through rock much faster, so it arrives first and rarely does damage. The S wave, arriving after it, produces most of the shaking that cracks walls and throws objects off shelves.
California has placed a network of sensors across the state to listen for P waves. When several sensors near the start of an earthquake detect one, computers estimate where the quake began and how strong it is, and then send out an alert. Electronic signals travel far faster than any wave through rock, so the alert can outrun the shaking.
How much warning a person gets depends on distance. Someone far from where the earthquake began may have twenty seconds or more. Someone very close may get no warning at all, because the strong shaking reaches them before the system has finished its calculation. This is one reason the system matters most for large earthquakes: a large quake shakes a wide area, so many people are far enough away to benefit.
A few seconds are enough for more than most people expect. A person can drop to the ground, take cover under a sturdy table and hold on, which protects against the most common earthquake injuries, those caused by falling objects. Trains can begin to slow down. Elevators can be programmed to stop at the nearest floor and open their doors. A surgeon can lift an instrument away from a patient.
None of this makes an earthquake harmless. But it turns the first moments of one from a complete surprise into something people have a few seconds to meet.
The question
Choose the best answer.
Why does the author include the examples of trains, elevators and a surgeon in the fifth paragraph?
- To argue that hospitals and transit systems should pay for the sensors.
- To show that only large organizations benefit from the warning system.
- To explain why the S wave causes more damage than the P wave.
- To show that even a few seconds of warning can be put to practical use.Correct answer
Why “To show that even a few seconds of warning can be put to practical use.” is correct
This tests author's purpose: why a group of examples is there, not what any one of them says. The paragraph opens with its claim, 'A few seconds are enough for more than most people expect', and every example that follows is an action short enough to fit inside that window. Encourage students to read a paragraph's first sentence as the point its examples are meant to prove.
Why the other answers are wrong
- To argue that hospitals and transit systems should pay for the sensors. — The passage never discusses who pays for the system.
- To show that only large organizations benefit from the warning system. — The paragraph's first example is an ordinary person taking cover, so the benefit is not limited to organizations.
- To explain why the S wave causes more damage than the P wave. — The difference between P and S waves is explained in the second paragraph, not in this one.
Practice more of this
More reading practice for Grades 9–10, or see the ELPAC practice test for grades 9–10. For other grades, see free ELPAC practice tests by grade.
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