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

1. A.
   gained
2. B.
   to gain
3. C.
   having gained
4. D.
   gain

He is rather difficult to make friends with, but his friendship, _____ is more true than anyone else’s.

He is rather difficult to make friends with, but his friendship, _____ is more true than anyone else’s.

He is rather difficult to make friends with，but the friendship of his，________，is more true than any others'.

A．once gained　　 　　 B．when to gain

C．as gained　　 　 D．while gaining