题目

 I think _     ____necessary __    _____ to take more exercise.    A. it, for Jim and me     B. it’s, to Jim and me      C.that , for Jim and I    D. that’s, to Jim and I 答案：A19．用扳手拧螺母时，若用同样大小的力在A点和B点拧，在B点更容易拧紧或松一些，这表明力的作用效果与力的作用点有关．