In my mind, no such          thing in our country as          Great Wall can stand for the image and culture of China.

A．a; the

B．a; /

C．/; the

D．/; /

汽化水掏空极限深度是（）

A、油层顶界

B、油层底界

C、套管允许的最大掏空深度

D、没有限度