) did the realize that he had made a mistake.

问题描述:

) did the realize that he had made a mistake.
A.Upon entering the classroom
B.Only after entering the classroom
C.After he had entered the classroom
D.As soon as he entered the classroom
On(Opon) ing Upon entering the classroom,he realized that he had made a mistake.这句话对吗?

On(Opon) ing 不用倒装.
Upon entering the classroom,he realized that he had made a mistake.
这句话本身是对的.意思同:
The moment/As soon as he entered the classroom,he realized that he had made a mistake.