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问题 单项选择题

氟牙症的临床特点是

A．乳恒牙都多见

B．氟牙症严重程度和氟过量水平成反比

C．牙釉质变脆，牙本质正常

D．牙釉质耐磨性差，抗酸能力强

E．患氟牙症牙数的多少和牙发育矿化时期在高氟区生活时间的长短相关

答案

参考答案：D

完形填空

Cell phones are so cheap that almost all people can afford it. _____ you go, you can see people holding cell phones doing different things. Our life style has changed greatly  _____ of the widespread of mobile phones.

Mobile phones change _____ way we contact others. In the past, we contacted our families, relatives and friends by writing letters _____ just going to a certain area to make a phone call. Now, if we want to contact them, all we need to do is to take out our cell phone, dial the number and then we can reach _____ in a minute.

With a cell phone, we _____ take photos and locate ourselves easily. All cell phones have a camera function. We can take photos anywhere we want and do _____ need to take our camera. Besides, _____ we are lost, we can use a cell phone to locate ourselves and find the right direction.
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