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 the friendship of his，________，is more true than any others'.

A．once gained　　 　　 B．when to gain

C．as gained　　 　 D．while gaining

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

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

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 (2010年烟台检测)He is rather difficult to make friends with，but his friendship，________，is more true than any other’s.

A．once gained                         B．when to gain

C．after gaining                        D．while gaining