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A. Determining the main idea. Choose the best answer. Do not refer to the text. The main idea of the article is that ________.
A.
our sleep time over the past century has been reduced by about 20%
B.
sleep debt accumulates and harms our health and we need to adopt a sleep-smart lifestyle
C.
biological clock within us regulates sleeping and waking and sleep debt always exists
D.
sleep deprivation might lead people to make mistakes with tragic consequences