-There are many old houses in Beijing, aren't there?

-_______ Only a few remain now.[ ]

A.Yes, they are.

B.No, they aren't.

C.No, there aren't.

D.Yes, there are.

压力即物理作用，是卷杠在烫发过程中所应有的（）。

A.化学反应

B.作用力

C.拉力

D.分解作用