A Biological Clock
Every living thing has what scientists call a biological clock that controls behavior. The biological clock tells 1 when to form flowers and when the flowers should open1. It tells 2 when to leave the protective cocoons and fly away，and it tells animals and human beings when to eat, sleep and wake.
Events outside the plant and animal 3 the actions of some biological clocks. Scientists recently found, for example, that a tiny animal changes the color of its fur 4 _ the number of hours of daylight. In the short 5 of winter, its fur becomes white. The fur becomes gray brown in color in the longer hours of daylight in summer.
Inner signals control other biological clocks. German scientists found that some kind of internal clock seems to order birds to begin their long migration 6 twice each year. Birds 7 flying become restless when it is time for the trip, 8 they become calm again when the time of the flight has ended.
Scientists say they are beginning to learn which 9 of the brain contain biological clocks. An American researcher, Martin Moorhead, said a small group of cells near the front of the brain 10 to control the timing of some of our actions. These 11 tell a person when to 12 ，when to sleep and when to seek food . Scientists say there probably are other biological clock cells that control other body activities.
Dr. Moorhead is studying 13 our biological clocks affect the way we do our work2. For example, most of us have great difficulty if we must often change to different work hours.
14 can take3 many days for a human body to accept the major change in work hours. Dr. Moorhead said industrial officials should have a better understanding of biological clocks and how they affect workers. He said 15 understanding could cut sickness and accidents at work and would help increase a factory’s production,
词汇：
biological /baɪə(ʊ)"lɒdʒɪk(ə)l/ adj.生物(学）的
insect /"ɪnsekt/ n.昆虫
cocoon /kə"kuːn/ n.防护卵袋,茧
fur /fɜː/ n.软毛
migration /maɪ"greɪʃ(ə)n/ n.迁徙
restless /"res(t)lɪs/ adj.焦躁不安的
contain /kən"teɪn/ v.含有
cell /sel/ n.细胞
注释：
1. 本句中谓语动词tells的宾语由两部分组成。第一部分是when to form flowers，是带疑问副词的动词不定式，第二部分是when the flowers should open,是名词从句。从修辞上说，两者有些不平衡。
2. …the way we do our work 可以理解为 the way in which we do our work 或 the way that we do our work.实际上，三种说法都成立。如：
He speaks English the way the English people do.
I don’t understand the way in which he dealt with the matter.
3. take作“花费，花去”解时可用于几种不同的句型：
It will take me five days to complete the work.
The work will take me five days to complete.
To complete this work will take me five days.空12
A:awaken B:woke C:awakening D:wake-up
One Good Reason to Let Smallpox Live
It’s now a fair bet that we will never see the total extinction of the smallpox virus. The idea was to cap the glorious achievement of 1980，when smallpox was eradicated in the wild, by destroying the killer virus in the last two labs that are supposed to have it — one in the US and one in Russia. If smallpox had truly gone from the planet, what point was there in keeping these reserves?
1 reality, of course, it was naive to 2 that everyone would let 3 of such a potent potential weapon.1 Undoubtedly several nations still have 4 vials. 5 the last “official” stocks of live virus bred mistrust of the USandRussia,2 6 no obvious gain.
Now American researchers have 7 an animal model of the human disease,opening the 8 for tests on new treatments and vaccines. So once again there’s a good reason to 9 the virus —just in 10 the disease puts in a reappearance.
How do we 11 with the mistrust of theUSandRussia? 12 Keep the virus 13 international auspices in a well-guarded UN laboratory that’s open to all countries. TheUSwill object, of course, just as it rejects a multilateral approach to just about everything. But it doesn’t 14 the idea is wrong. If the virus 15 useful, then let’s make it the servant of all humanity — not just a part of it
词汇：
smallpox /"smɔːlpɒks/ n.天花
cap /kaep/vt.结束;覆盖
killer /"kɪlə/ n.杀死物;杀人者
potent /"pəʊt(ə)nt/ adj.有效力的;强有力的
vial /"vaɪəl/ n.小瓶
mistrust /mɪs"trʌst/ n.不信任，怀疑
auspices /"ɔːspɪsɪz/ n.赞助;支持
注释：
1.In reality, of course, it was naive to imagine that everyone would let go of such a potent potential weapon.当然,想象每个人都会放弃这样一种有效的潜在的武器事实上是幼稚的。
2.And the last “official”stocks of live virus bred mistrust of theUSandRussia...:美俄最后的“官方”活病毒储备引起大家对这两个国家的不信任。
空12
A:Difficult B:Hard C:Safe D:Simple
我国只有12个少数民族有沿用至今的传统文字，一共（）种。
A:12 B:13 C:14 D:15
制冷剂R12是使用广泛的一种制冷剂，被R134a取代的主要原因是：（）
A:R12破坏大气臭氧层 B:R12对人体伤害太大 C:R12的物理性质不稳定 D:本题其他答案都正确
T12和T8两种钢号材料比较（）。
A:T12的强度、硬度均高于T8 B:T12比T8的强度高而硬度稍低 C:T12比T8的强度稍低而硬度却高 D:T12比T8的强度稍高而硬度也高
内燃机的15min功率、1h功率、12h功率和持续功率四种功率中，最小的是（）。
A:15min功率 B:1h功率 C:12h功率 D:持续功率
某经济学院从国外引进了30种教材，其中，金融类教材12种，非金融类的英文教材10种，从美国引进的非金融类教材7种，从美国以外国家引进的非英文教材9种。
根据上文，可以推知（ ）
A:从美国引进的、非英文的金融类教材不超过8种 B:从美国引进的、非英文的金融类教材至少有8种 C:从美国以外国家引进的、非英文的金融类教材不超过8种 D:从美国以外国家引进的、非英文的金融类教材至少有8种
某经济学院从国外引进了30种教材，其中，金融类教材12种，非金融类的英文教材10种，从美国引进的非金融类教材7种，从美国以外国家引进的非英文教材9种。
根据上文，可以推知（ ）
A:从美国引进的、非英文的金融类教材不超过8种 B:从美国引进的、非英文的金融类教材至少有8种 C:从美国以外国家引进的、非英文的金融类教材不超过8种 D:从美国以外国家引进的、非英文的金融类教材至少有8种
PLC考试
