题目

Many people ______ in traffic accidents in the past few years. A. killed         B. are killed        C. were killed     D. have been killed   答案：D（6分）如图所示，一个重600N的人用200N的力通过绳子和定滑轮拉一个静止在地面上重600N的物体M，则人受到            ，                  力和              力作用，其大小分别为                N，                   N和                     N。