How does caffeine keep us alert
Reading
Read the text and answer the multiple-choice question by selecting the correct response. Only one is correct.
Passage
Caffeine works by blocking a chemical in the brain that makes us feel sleepy. This is why a cup of coffee can leave us feeling alert. However, as the effect wears off, that chemical can flood back, sometimes producing a sudden sense of tiredness.
How does caffeine keep us alert?
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