题目

Yesterday I went to see him, _________ that he had gone abroad two days before. A. only to learn    B. to learn only    C. only learned    D. only learning 答案：A11．粗糙水平面上静止一质量为4kg的物体，用大小为12N的水平力使物体运动2m后撤去拉力，物体又滑动了4m停止．求：（1）在这个过程中拉力对物体做的功；（2）水平面的动摩擦因数．