已知M（－3，0），N（3，0），|PM|－|PN|=4，则动点P的轨迹是：（）

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问题选择题

A．双曲线

B．双曲线左支

C．双曲线右支

D．一条射线

答案

答案：C

|MN|="6" ，∴|MN|>|PM|－|PN|>0 ∴动点P的轨迹是双曲线右支

单项选择题 A1型题

嘌呤环中的N7来源于（）

A.AlA

B.Asp

C.Gln

D.Glu

E.Gly

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听力题

Do you know an old city called "Pingyao" in Shanxi? The old city is not f___ from Taiyuan. It's a town with a long history of more than two t____ years.

The old city is not very large. It is only 2.25 s__ kilometers in size. And there are no tall buildings here. Most of the buildings have only two f___. And most of them are m______ of stones(石头). There are many Chinese-style shops on either side of the street.

Pingyao is a square city. The city has a wall a_____ it. It's about 6 km long and 12 m high. The wall has six gates. And you mustn't m____ the nice food in Pingyao. Try Pingyao beef and you are s__ to fall in love with it.

Pingyao is a place worth(值得) a visit. You can take buses or trains here. It's less than 2 hours' bus ride from Taiyuan. It c__ you only 20 yuan. If you take a train, it will take you less time, only one and a half hours. And if you want to go to Pingyao from Beijing, the train ride takes o_____ about 6 hours.

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