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问题 选择题

电孵化箱可取代母鸡大规模繁殖小鸡，其作用原理是提供了（　　）

A．适宜的温度

B．充足的氧气

C．适宜的水分

D．充足的光照

答案

受精的鸟卵在雌鸟时，精子和卵细胞就已经结合形成了受精卵，胚胎发育就已经开始，它就是鸟卵中色浓而大的胚盘，而未受精的卵，胚盘色浅而小．鸟卵产出后，由于外界温度低于雌鸟的体温（鸟类的体温约为40℃），胚胎发育就会暂时停止，而温度达到鸟类的体温，可雌鸟孵化，也可人工孵化，胚胎发育将会继续进行，最终发育成雏鸟．电孵化箱可取代母鸡大规模繁殖小鸡，其作用原理是提供了适宜的温度．

故选：A

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     School education(教育) is very important and useful. Yet no one can l  1   everything at school and a

teacher can't teach his students e  2   they want to know. His job is to s  3   his students how to learn. He

teaches them how to read and how to think. So the students can learn much more by t  4  .

     It is more i  5      to know how to study by  oneself.  It's quite easy to learn something, but it's difficult

to u  6   it to solve problems. Great inventors  do  not get everything from school, but they still can invent

many things and change the world a l  7  .

     How can the inventors do all of this? That's b  8      they know how to  study. A lot of things are not

taught in the classroom. They   get a lot of knowledge by reading o  9     school. They  work  hard  and

never g  10   up all their lives.

1. l         2.e         3. s         4.t         5. i          

6. u             7.l           8.b         9.o         10.g          
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单项选择题

设随机变量X服从正态分布N（-1，9），则随机变量Y=2-X服从（）．

A.正态分布N（3，9）

B.均匀分布

C.正态分布N（1，9）

D.指数分布
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