水泥混凝土路面的缺点有（）。
A.强度高
B.稳定性好
C.开放交通早
D.耐久性好
参考答案：C
She said she _______ the new coat for only a week.[ ]
A. has bought
B. had bought
C. has had
D. had had
如图所示，粗细均匀的U形管内装 有同种液体，开始使两边液面高度差为h，管中液柱总长为4h，后来让液体自由流动，当两液面高度相等时，右侧液面下降的速度为
A．
B．
C．
D．
