The word “it” in paragraph 2 refers to ______. A. action B. caffeine C. reason D. brain
Giải thích
Giải thích: B
Từ “it” thay thế cho từ “caffeine”.
The reason that caffeine makes you feel alert and less sleepy is because it blocks the action of adenosine, the brain chemical which controls your sleep patterns, and increases adrenaline production, speeds your metabolism.