It’s true that teens don’t get enough sleep, but changing the school starting time would have a chaotic effect and throw everyone off balance.

Scientists have shown that teens are more active later at night than children and adults, so most teens are probably staying up later for whatever reasons. The researchers measured the presence of the sleep- promoting hormone in teenagers' saliva（唾液）at different times of the day. They learned that the hormone（荷尔蒙）levels rise later at night than they do in children than adults and remain at a higher level later in the morning. Measuring the hormone in the saliva is a good way to show that most teens have sleep problems, but changing schools schedules isn’t the best way to do to fix this. Most people arguing against changing school schedules would say that it would only cause teens to stay up and wake up later, thus leaving them with the same problem.

The biggest problem schools would come across from changing their schedules would be the after school and job conflicts students and teacher would meet. Teachers reported that students were more alert, and research showed that after-school sports and jobs would suffer. Students in that area might have been able to deal with less time for jobs and sports somehow, but some of them have practice and earlier plans that would become conflicted if this change were to occur. Most students rarely have time to play a sport and do homework before 9 or 10 o'clock. Opening schools later may have worked for some areas, but the reality is often very different.

63. The meaning of the underlined word "chaotic "（in the 1st paragraph）is close to_______.

A. positive                B. apparent                   C. negative                   D. definite

64. Most teens have sleep problems because ________.

A. they are more active than children and adults

B. school work takes up most of their time

C. their hormone levels are higher later at night

D. they probably like staying up for no reasons

65. Which of the following is TURE according to the passage?

A. There are many conflicts between students and teachers

B. Some of the teachers have practice and earlier plans

C. Most students are able to do sport and homework before 9:00

D. Ways to solve students' sleep problems depend from area to area

66. The passage mainly develops by ________.

A. giving reasons                B. showing examples

C. presenting questions        D. offering solutions