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问题 选择题
已知函数f（x）=xn，其中n∈Z，n≥2．曲线y=f（x）在点P（x0，f（x0））（x0＞0）处的切线为l，l与x轴交于点Q，与y轴交于点R，则
|PQ|
|PR|
=（　　）
A．
1
n-1
B．
1
n
C．
2
n-1
D．
2
n
答案

由题可得f′（x）=nxn-1．

所以曲线y=f（x）在点（x0，f（x0））处的切线方程是：y-f（x0）=f′（x0）（x-x0）．

即y-x0n=nx0n-1（x-x0）．

令y=0，得-x0n=nx0n-1（x-x0）．

x0＞0，

∴x=x0-

x0
n
，得l与x轴交点Q（x0-
x0
n
，0），如图．

则

|PQ|
|PR|
=
|PA|
|PB|
=
|x0-
x0
n
-x0|
|x0|
=
1
n
．

故选B．

补全对话，情景问答
补全对话(从七个选项中选出五个，完成以下对话）。
A. I like the city very much.              B. Is it hot there in summer?
C. Can you swim here?                     D. Have you ever been there?
E. Sorry! I have no time.                   F. Do you like the city?
G. What do you think of the city?
A: I want to spend my holidays in Dalian. 1            .
B: Yes, I have been there many times.
A: 2           .
B: Yes, I like the city very much. She's coming one of the most modern cities in the world.
A: 3           .
B: The city is clean and beautiful. The people are kind and the football team is strong.
A: 4           .
B: No, not very hot. You may have a swim in the sea.
A: How cool! Swimming in the sea must be more wonderful than in the lake.
B: I'm sure you'll have a good time there.
A: Would you please go with me?
B: 5           .
A: What a pity!
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问答题 简答题

制定《安全生产法》的目的是什么？
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