阅读理解。

     We all know that teenagers like to sleep late. But more and more research is showing that this is not just

a preference-or even the result of late-night studying or instant messaging-but is rooted in their biological

rhythms(节律). All of this would be little more than an interesting observation except that most high schools

start so early, and so many teenagers are having a hard time staying awake.

     A recent article in The Times cited a National Sleep Foundation survey in which more than a quarter of

the students reported that they fell asleep in class at least once a week. Researchers say this is true because

youngsters - beginning around age 12 until they reach their mid-20s-only start producing melatonin, the

sleep-inducing hormone(荷尔蒙), around 11:00 pm and that production lasts until about 7:00 am. In adults,

melatonin lasts to around 4:00 am. Trying to wake up a teenager before 7:00 am is like trying to awake an

adult before 4:00 am.

     The obvious remedy(补救)would be for high schools to start later-well, after 8:00 am. A handful of

schools that have switched have reported beneficial results. School officials in Minneapolis say that

attendance improved and students' grades rose slightly after they changed to start at 8:40 am several years

ago. In Wilton, Conn., where the high school start time was pushed back to 8:20 am from 7:35 am, teachers

and parents reported better student behavior and greater alertness. Surveys of students in both districts

indicated that they did not use the later starts as an excuse to go to bed later.

     Numerous districts have considered the idea of later high school hours, only to drop it because of fierce

adult opposition. Coaches complain that the later classroom hours in the afternoon would take time from

their training programs and teams' success. School bus companies would be forced to change their

schedules. And many parents complained that they would have to adjust their own schedules.

     Many schools officials say more research is needed. We're all for that and for remembering that the goal

is to educate youngsters-and for that they need to be awake.

1. According to the new research, teenagers like to sleep late because ______.

A. they have to study till late at night

B. they waste too much rest time sending instant messages

C. they prefer to stay in bed rather than get up early

D. their biological systems make them do so

2. We can learn from the second paragraph that melatonin makes _______.

A. youngsters awake after 7:00 am

B. adults sleepy after 4:00 am

C. youngsters sleepy before 7:00 am

D. adults awake after 4:00 am

3. The third paragraph is written to show that _____.

A. many high schools start after 8:00 am

B. later high school start time made students go to bed late

C. students don't go to bed late even though they have later high school hours

D. later high school start time is a very effective measure

4. According to the passage, who are fiercely against later high school hours?

① School team coaches.

② Many parents.

③ School teachers.

④ School bus companies.

A. ①②③

B. ①②④

C. ①③④

D. ②③④

5. We can infer from the passage that the author's attitude towards later high school hours is _____.

A. positive

B. negative

C. indifferent

D. unclear