下列属于复习的外部手段的是（）。

A.做笔记

B.做读书卡片

C.标记重点内容

D.听说读写相结合

A．(A) Because he could avoid being killed by the H-bomb.

B．(B) Because he had a new world to fight for.

C．(C) Because he was able to enjoy a pollution-free life.

D．(D) Because he succeeded in setting up his own business.