A bird was seen___(fly)into the classroom yesterday.

问题描述:

A bird was seen___(fly)into the classroom yesterday.

A bird was seen_flying/ to fly__(fly)into the classroom yesterday
可以选这两种,用flying表示看到正在飞进去,但没有看到全过程
选to fly表示看到了全过程,同时因为用于被动语态,所以不定式的to 要填上