对于随机变量X，Y满足D（X）=0.3，D（Y）=0.2，cov（X，Y）=0.1，

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问题单项选择题

对于随机变量X，Y满足D（X）=0.3，D（Y）=0.2，cov（X，Y）=0.1，则D（X+Y）=（）

A.0.5

B.0.6

C.0.7

D.1

答案

参考答案：C

填空题

根据句义和首字母写出所缺的单词。

1. Kate's glass is empty. She wants a f______ one.

2. I think my father can help you m______ your broken bike.

3. I have two pencils. One is short, the other is l______.

4. Please open the w______. It's getting hot here.

5. Something is w______ with my bike. May I borrow yours?

多项选择题

干净光滑物面上的加层油脂手印，可用（）来显现。

A、铝粉

B、磁性粉

C、硝酸银

D、茚三酮