When he was a boy, he used to go there and watch .
A. to repair bicycles
B. bicycles to be repaired
C. bicycles being repaired
D. repairing bicycles
网友回答
A. to repair bicycles
B. bicycles to be repaired
(答案→)C. bicycles being repaired
D. repairing bicycles
解析：用-ing形式一般式的被动语态作宾语补足语，强调自行车被修理的过程。