有关牙齿松动，哪项是错误的（） A.生理状态下，牙齿不松动 B.急性根尖周炎可使牙松
题型：单项选择题
问题：
有关牙齿松动，哪项是错误的（）
A.生理状态下，牙齿不松动
B.急性根尖周炎可使牙松动
C.妊娠期、月经期牙齿可出现松动
D.长期口服激素类避孕药的妇女可出现牙齿松动
E.急性牙外伤可使牙松动
题型：单项选择题
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| Perhaps you ride a bicycle to school. Riding a bicycle can be great fun. Do you know how to ride a bicycle 1 ? Careful boys and girls learn to ride their bicycle well 2 they go out on the road. How can you tell 3 you are a good rider? If you can ride a bicycle in a straight line, you can ride well. If you can't ,you should practise riding 4 a safe place. To be safe on a bicycle, you 5 to use both hands and both feet. 6 your feet on the pedals and your hands on the handle bars at all times. Do you have a basket on your bicycle? If so, put your books and packages in it. Then you can 7 both hands on the handle bars. You know that your bicycle is built for one person. It is not safe to carry anyone 8 you. 9 is this so? Keep 10  safe by safety rules when you ride on a bicycle. Watch where you are going at all times. | |||
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