He is not easy-going but his trust in his friends will last forever once .A. to be gaine

问题补充：

He is not easy-going, but his trust in his friends will last forever once .

A. to be gained

B. is gained

C. being gained

D. it is gained

答案：

A. to be gained

B. is gained

C. being gained

(答案→)D. it is gained

解析：考查状语从句的省略式：当主从句的主语一致的时候，可以省略从句的主语和be动词，句意：他不是很随和，但是他对朋友的信任一旦获得就永远不会消失。这里的it指代his trust in his friends，如果省略的话，应该是填gained，ABC都不对，所以就不用省略式，选D。