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问题 选择题
若f（x）=-
1
2
x2-2x+blnx在[1，+∞）上是减函数，则b的取值范围是（　　）
A．（-∞，-1]B．[-1，+∞）C．[3，+∞）D．（-∞，3]
答案

f′（x）=-x-2+

b
x
，由于f（x）在[1，+∞）上是减函数，所以f′（x）≤0在[1，+∞）上恒成立．

所以-x-2+

b
x
≤0，b≤x（x+2）令g（x）=x（x+2），x∈[1，+∞），只需b≤g（x）min．

g（x）=（x+1）2-1在[1，+∞）单调递增，g（x）min=g（1）=3，所以b≤3，b的取值范围是（-∞，3]

故选D

完形填空

根据下面短文内容填空，每空限填一词。

The students were having their chemistry class. Miss Li was telling the children what water was like. After that, she asked her students, “What is water?” No one answered for a few minutes. Miss Li asked again, “Why don’t you answer my question? Didn’t I tell you what water is like?”

Just then, a boy put up his hand and said, “Miss Li, you told us that water has no color and no smell. But where to find such kind of water? The water in the river behind my house is always black and it has a bad smell.” Most of the children agreed with him.

“I’m sorry, children,” said the teacher, “Our water is getting dirtier and dirtier. That’s a serious problem.”

小题1:Miss Li was telling her students about         in a             class.

小题2:Miss Li asked the students the same question        ,        no one answered.

小题3:We know that water doesn’t         color        smell.

小题4:A boy      Miss Li that the water in the river behind       house was always black.

小题5:Miss Li felt         because the water        getting dirtier and dirtier.

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单项选择题

下列哪一项是矫形鞋的基本作用

A．减轻疼痛

B．预防畸形的发展

C．消除关节活动

D．代偿丧失的关节功能

E．上述四项都对
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