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问题 选择题
一个正四棱锥的底面面积为Q，则它的中截面（过各侧棱的中点的截面）的边长是（　　）
A．
Q
2
B．
Q
4
C．
Q
D．
Q
4
答案

由棱锥的几何特征可得

棱锥的中截面与棱锥的底面是相似图形

且相似比为

1
2

则棱锥的中截面与棱锥的底面的面积之比为相似比的平方

1
4

又∵棱锥的底面面积是Q，

∴棱锥的中截面面积是

Q
4
，则它的中截面的边长是
Q
2

故选A．

多项选择题

线性放大测量适合于检测（）。

A.细胞膜表面抗原的分布

B.单核细胞含量

C.总蛋白质含量

D.RNA含量

E.DNA含量
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填空题



Every human being is fallible; we make mistakes. In America when a mistake has been made, it is considered fitting for the person (1) to acknowledge his or her error and to apologize to anyone who has been inconvenienced. Even (2) are expected to admit their mistakes and apologize for them. Trying to (3) a mistake and denying your guilt are considered to be indicative of serious (4) .
If you make a mistake that (5) a group of people, a public apology is considered the best method for (6) . If the mistake was a serious one, or if some people were inconvenienced more than others, then the (7) should follow the public apology with private ones to (8) .
It is especially important for executives and company heads to be able to admit their mistakes. Sometimes leaders are afraid that if they (9) , they will lose the respect of their employees. Actually (10) — if you are honest with your employees and yourself, (11) , and show that you are willing to accept blame when you make a mistake, then your employees will be (12) you. They will also be more likely to admit their own mistakes.
If you (13) one person, it is usually best to apologize to that person alone, unless your mistake (14) by a large group of people. For example, if Leonard (15) to Mr. Todd during a committee meeting, it would be (16) for Leonard to apologize to Mr. Todd at the next committee meeting. If the (17) created by the initial mistake is public, then the apology should be public. However, if Leonard raised his voice to Mr. Todd when only the two of them (18) , he may apologize privately. Notice as well (19) the apologies are. As soon as you realize you have made a mistake, you should (20) .
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