对飞机上面积很小的空速管、静压孔和失速传感器叶片等探头，除冰方式通常采用：（）.
A.气热防冰
B.电热防冰
C.化学防冰
D.气动防冰
参考答案：B
老子说：“天下难事，必作（注：开始）于易，天下大事，必作于细。”这句话蕴涵的哲学道理是 [ ]
A、事物的变化发展先从量变开始的
B、重大的事件都是由小事件构成的
C、微小的事情必定会发展为重大事情
D、量变积累到一定程度才能引起质变
I wrote a letter to John for his help during my high school years. without which I the college entrance exam.
A． would fail
B．would have failed
C．should fail
D．must have failed
