题目

．Have you considered the students’ request _________ the school library _______ more books on popular science? A. that  ; provide            B. when ; provided     C. which ; should provide     D. where; would provide 答案：A3．用“一动、一定”组成的滑轮组来匀速提升重物时，所需要的力与不使用滑轮组直接提升重物时相比较，可省$\frac{1}{2}$或者$\frac{2}{3}$的力．