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．/; /

起钻最大量的抽吸作用，发生在钻头（）的时候。

A.经过套管鞋

B.经过缩径井段

C.经过狗腿处

D.刚离开井底