题目

--Who is the old man talking with your teacher?   ---I don’t know. I     him before. A. was never seeing   B. had never seen   C. never saw  D. wouldn’t see 答案：C如图14所示，一辆汽车陷入泥淖，为了将它拖出，司机用一条长41m的绳一端系于车前钩，另一端系于距车40m处的一棵大树上，然后在绳之中点用900N的力F向垂直于车与大树联线方向拉绳，将车拖出，试求汽车所受拉力的大小。