如图3-7-6所示,质量为M的框架放在水平地面上,一根轻质弹簧的上端固定在框架上,下端拴着一个质量为m的小球,在小球上下振动时,框架始终没有跳起地面.当框架对地面压力为零的瞬间,小球加速度的大小为( )图3-7-6
Hey,Jane.______ are you feeling now?
Much better.Thanks.( )
A.WhatB.WhereC.HowD.When
This museum ______ here for over 80years.It ______ one of the oldest buildings in this city.( )
A.is; wasB.had been; is
C.was; has beenD.has been; is
Xiandao Lake in Yangxin is the famous place ______ we'll visit next week.( )
A.thatB.whoC.whereD.whom
Sorry,Miss Liu.I left my workbook at home.Must I hand it in today?
No,you ______.You ______ bring it here tomorrow.( )
A.mustn't; shouldB.can't;must
C.mustn't;mayD.needn't;can
The twins look exactly the same.______ of them are in my class.( )
A.EachB.BothC.EitherD.None