D. Complete this summary using the words from the article.
(Hoàn thành bản tóm tắt này bằng cách sử dụng các từ trong bài viết.)
Sleep is good for physical and (1) mental health. It helps stop (2) _____ and keeps us healthy. We also study and work (3) _____ when we sleep for (4) _____ hours. But in the twenty-first century, we aren't getting enough sleep. One reason is that we stay up (5) _____ or (6) _____ all night. Another reason is that (7) _____ light from screens keeps us awake. As a result, medical experts advise us to stop looking at screens (8) _____ hour before bed.