He is not easy toget along with, but the friendship of his, ________, will last forever.

A.oncegained

B.to begained

C.aftergained

D.whilegaining

答案及解析： A

解析：

gain与friendship是被动关系，用过去分词。译文：他很难相处，但是一旦获得了他的友谊，就永远不会失去了。