题目

根据对话内容，从方框内选择恰当的句子将对话补充完整。（选项中有两项是多余的）A: What will you do during the coming summer holiday, Lingling?B: Traveling. It’s my favorite hobby.【1】 A: I’m not sure. In fact, I’d like to be a volunteer. B: A volunteer? Why would you like to be a volunteer?A:【2】B: What will you do exactly?A: Perhaps teaching. You know my parents are teachers. If necessary, I can ask them for help. B:【3】A: Some villages in the mountains which are not far from here. B: Why?A: Because I have learned a lot about the children ther在光滑水平面上有一弹簧振子，弹簧的劲度系数为k，振子的质量为M,振动的最大速度为v0，如图9-1-7所示，当振子在最大位移为A的时刻，把质量为m的物体轻放在其上，则: 图9-1-7（1）要保持物体和振子一起振动，二者间的动摩擦因数至少为多大？（2）二者一起振动时，二者过平衡位置的速度为多大？