题目

Trapped under ruins after the Iran earthquake, Dan Woolley believed he was going to die. But rather than giving up, the film-maker managed to look up ways to treat his injuries on his iPhone beneath the earth. He also wrote a moving diary for his family, allowing them to read his last messages of love and comforting them after his death. Instead, he was pulled from the ruins after a week--- and would soon meet his family. Mr. Woolley, from Colorado Springs, America, had raveled to Iran with his colleague David Hames. Both had been working for Charity Compassion International. He was i如果适当地把n种简单机械组合使用，就（ ）A．一定省力B．一定省功C．一定能省距离D．一定不省功