有些动词后跟不带to的不定式作宾语补足语,但改为被动结构后要加上“to”.例如
1、We heard him sing in his room just now.
---He was heard to sing in his room just now.
2、A girl saw my wallet drop when she passed by.→My wallet was seen to drop by a girl when she passed by.
3、The boss made the little boy do heavy work.→The little boy was made to do heavy work by the boss.