（1）What can cause problems in students' study？
A.Quarreling with their parents.
B.Arriving late for class.
C.Not getting enough sleep.
（2）Who thinks that students should have 9 hours' sleep every night？
A.Parents.
B.Teachers.
C.Scientists.
（3）Why do most students feel nervous and forgetful？
A.Because they worry about their study.
B.Because they don't get enough sleep.
C.Because they often get lower grades.
（4）Why do most students go to bed late？
A.Because there may be too much noise in their bedrooms.
B.Because there may be parents in their bedrooms.
C.Because there may be computers in their bedrooms.
（5）When do many students go to sleep？
A.Before 10 p.m.
B.After 11 p.m.
C.At about 9 p.m.