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问题 选择题

真空中，带电量为Q的点电荷产生的电场中，在距离点电荷r处放置一试探电荷，若试探电荷电量为q，则该处的场强大小为（　　）

A．0

B．

kq
r2

C．

kQ
r2

D．与放在该点的试探电荷有关系

答案

A、点电荷周围存在电场，电场强度不会为零，故A错误

B、由库仑定律得：F=K

Qq
r2
，且E=
F
q
，故E=k
Q
r2
，故B错误

C、由B分析得，C正确

D、电场强度与试探电荷无关，故D错误

故选C

阅读理解

读短文，根据短文内容选择正确答案。

      Mike comes from America. He is twelve. His father Mr. Brown works in a big shop in Beijing. Mike has a

sister. Her name is Kate. She is only four.

      It is Saturday today. Mike's family is at home. Mr. Brown is sitting in a chair and reading today's newspaper.

Mrs. Brown is out of the house, and she is watering the flowers. Is Mike with his mother? No, he is cleaning his

new bike. Where is Kate? She is in her room. She is playing with her cat. What a happy family!

1. Mr. Brown works ______________.

A. in America

B. in a bank

C. in Beijing

D. at home

2. Who is Kate?  She is ______________. 

A. only four

B. Mike's sister

C. playing

D. at home

3. Mrs. Brown is ______________.

A. in the house

B. cleaning her new bike

C. sitting in a chair

D. watering the flowers

4. Mike is ______________.

A. cleaning his new bike

B. with his mother

C. in his room

D. sitting in a chair

5. Kate is playing with ______________.

A. Mike

B. Mr. Brown

C. Mrs. Brown

D. her cat
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单项选择题

常用的聚类方法有样品聚类法、系统聚类法和（）

A．

B．

C．回归聚类分析

D．平共处模糊聚类法
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