We should admit the fact that some families still can not afford their children going to school education, university ________.

A．in particular

B．in expectation

C．in charge

D．in certainty

百米运动员跑到终点时，不能立即停下来，这是因为运动员有______．锤头松了，将锤柄的一端在石墩上撞击几下，锤头就能紧套在锤柄上，这种做法是利用了锤头的______．