Walking down the street the other day, .
A. I saw unusual something happened
B. a terrible accident happened
C. something unusual was seen by me
D. I saw a terrible accident
网友回答
A. I saw unusual something happened
B. a terrible accident happened
C. something unusual was seen by me
(答案→)D. I saw a terrible accident
解析： 现在分词是主语的动作，因此I做句子的主语；修饰不定代词时，形容词要后置。