He is rather difficult to make friends with but his friendship is more true than any o

问题补充：

He is rather difficult to make friends with, but his friendship, , is more true than any other.

A. once gained

B. when to gain

C. after gaining

D. while gaining

答案：

(答案→)A. once gained

B. when to gain

C. after gaining

D. while gaining

解析：短语辨析. A. 一旦获得了;B. 什么时候得到C.得到后D. 而获得.句意:和他交朋友相当困难,但是他的友谊,一旦获得了,就比其他任何人的都真实.选A.