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下图表示人类镰刀型细胞贫血症的病因：

在DNA复制过程中，由于出现“差错”，导致DNA（）发生局部改变，从而改变了遗传信息。

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参考答案：内部结构（或碱基对序列）

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I have many pen pals in many countries.

Bill is my first pen pal .He is 13 years old. He is from Singapore. He lives with his grandparents .He has a big family.

Reiko is a little girl. She is Japanese .She is only 10 years old, but she can speak French and English.

Mike is  from Australia .He often talks to me on the Internet(互联网) .He likes basketball very much. His favorite basketball star is Michael Jordan.

Sally lives in New York of the USA. She is my new pen pal. She is very kind .She has many pen pals in China. She likes writing to them.

Gao Yu is also my pen pal .But he is a Chinese boy .He is in Beijing and he often calls me on weekends. We talk about something interesting in school.

小题1:How old is Bill?

.

小题2:What other languages can Reiko speak?

.

小题3:Where does Sally live?

.

小题4:Where is Gao Yu from?

.

小题5:What’s Mike’s favorite sport?

.
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单项选择题

使用正扣可退式打捞矛打捞时，如落鱼卡死，需退出打捞矛时，只要给一定的下击力，再（），上提钻具即可退出落鱼。

A.正转钻具2～3圈

B.反转钻具2～3圈

C.直接上提钻具

D.先正转再反转
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