SAT OwlQuestion bank / Text Structure and Purpose
Because the brain uses about a fifth of the body's energy, some people have assumed that thinking hard, as during a difficult exam, must burn noticeably more calories than resting. Measurements tell a different story. Brain imaging studies show that demanding mental tasks raise the brain's energy use only slightly above its already high baseline, by a few percent at most. The exhaustion people feel after hours of concentration, researchers now suggest, likely reflects changes in motivation and attention rather than a drained fuel supply.
Which choice best states the main purpose of the text?
To argue that the brain uses far less of the body's energy than researchers once believed
To describe how brain imaging studies measure the energy that the brain uses
To question a common assumption about mental effort and suggest another cause of mental fatigue
To recommend ways for students to avoid mental exhaustion during long, difficult exams
Show answer and explanation
Answer: C
The text starts with an assumption that sounds sensible (hard thinking burns many more calories), shows that measurements don't support it, and closes with a different explanation for mental fatigue. That is choice C.
Choice A misreads the text, which accepts that the brain uses about a fifth of the body's energy; it questions only how much extra hard thinking adds.
Why the other choices are wrong
- A. The text accepts that the brain uses about a fifth of the body's energy. It questions how much extra a hard task adds.
- B. Brain imaging is only a source of evidence. The text never explains how the studies work.
- D. Exams are just an example. The text gives no advice about avoiding exhaustion.
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