(1---7) AABDA DA
8. built-in pesticides
9. their genetic modification of a plant
10. safety and environmental impacts
A: 11—20 DBACD ACDAB
B: 26—35 DACCA BDDBC
Medical research is leading American education officials to consider having high school classes start later in the morning. The research says teenagers are more;36； awake later at night than adults are. When teenagers stay up late at night they have problems learning early in the morning.
Researchers in the state of Rhode Island measured the;37； presence of
the hormone;荷尔蒙； melatonin ;褪黑素；in peoples’ mouths at different
times of the day. Melatonin;38； causes people to feel sleepy.
They found that melatonin levels rise later at night in teenagers than they do in children and adults. And they;39； remain at a higher level in teenagers
later in the morning. They say this shows that teenagers have difficulty learning early in the morning. Yet most school;40； systems in the United
States begin high school classes at about seven o’clock.
A few school districts have made some changes. In nineteen ninety-six, school officials in Edina, Minnesota changed high school;41； opening from
about seven thirty until eight thirty. Two years later, the ;42；nearby city
of Minneapolis did the same. Teachers there;43； reported that students
were no longer sleepy in class and were happier.
;44； Health experts say teenagers need between eight and nine hours of sleep a night. Students who do not get enough sleep are likely to be late for school, fail to do their homework, fall asleep in class and have trouble taking part in class discussions.
;45；Yet some adults oppose changing school start times. because they say it would limit the time for practicing sports after school.
However, the Minnesota schools found that this did not hurt school sports competitions.
;46；More American school districts are discussing the possibility of changing high school start times. Researchers and teenagers say they
cannot make the change quickly enough.
47-56 KFBJI GAHEN
87. There seemed to be some differences 88. cares, fears, tears and doubts 89. In order to make it quite safe for him to go there
90. The problem of population control 91. I will broadcast at nine tonight.