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单选题
Because airplanes are intended to have long lives, their flight safety must be assured.
A
In order to make airplanes have long lives, they are often in good condition.
B
To make airplanes have long lives, it is necessary to ensure their flight safety.
C
Because the long lives of airplanes are required, make sure the mechanics do the maintenance task correctly.
答案解析
正确答案：B
