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问题 选择题
已知函数f（x）=log2x（x＞1），若f-1(a)•f-1(b)=2，则
1
a
+
4
b
的最小值为（　　）
A．4B．5C．8D．9
答案

∵f（x）=log2x（x＞1）

∴f-1（x）=2x（x＞0）

∴f-1（a）f-1（b）=2a+b=2

∴a+b=1

∴

1
a
+
4
b
=(a+b)(
1
a
+
4
b
)=5+
4a
b
+
b
a

∵

4a
b
＞0，
b
a
＞ 0

∴

1
a
+
4
b
≥5+2
4a
b
×
b
a
= 9（当且仅当
4a
b
=
b
a
即a=
1
3
，b=
2
3
时取等号）

故选D

完形填空

Good evening, here is the weather report. The weather tomorrow is vrey changeable. It will be sunny in the morning in Beijing. But in the afternoon, the weather will be rainy. In Shanghai, skies will be clear and you can enjoy the bright sunshine in the moning. But it will be clould with no sunshine in the afternoon. In Shenzhen , there will be a light right rain with winds in the morning, and in the after noon it will rain heavily.

1.It will be sunny in the morning in Beijing and      .

2.It will       in Beijing and Shenzhen tomorrow.

3.If you want to go to the park tomorrow in Beijing, you’d better go there in the      .

4.It will be       in the aftenoon in Shanghai.

5.It will be rainy and       in Shenzhen tomorrow.
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问答题

对比一下明朝郑和下西洋，引进外国作物和清朝闭关锁国的不同后果，谈谈你的想法。

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