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问题 填空题

年轻恒牙的牙根未完全发育，要在萌出后（）年才达到应有长度，而（）年后根尖孔才缩窄。

答案

参考答案：2～3‖3～5

选择题
Which of the following sentences is wrong?

A. When he was five, he had to look after his sister.
B. At the age of fifteen years old, he left school.
C. He won a gold medal at the last Olympic Games.
D. The boy doesn't play computer games anymore.
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单项选择题

柴油机设增压器的目的时为了使进入气缸的空气预先进行（）。

A.冷却

B.预热

C.压缩

D.稀释
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