题目

The man became a famous writer when he was ________.   A. in his fifty        B. in his fifties C. in fifty years old  D. in fifties 答案：B在验证“互成角度的两个力的合成”的实验中，某小组的出如图所示的图（F与A、O共线），其中A为固定橡皮条的图钉，O为橡皮条与细绳套的结点，图中    是F1与F2合力的理论值；图中     是F1与F2合力的实际值．