改错on seeing the boy fell into ther river,she sprang to her feet and went to the rescue.

题目

改错on seeing the boy fell into ther river,she sprang to her feet and went to the rescue.
这道题是fell错了吧,是不是应该把fell改成falling,但是我有点弄不明白非谓语动词为什么要用falling,而不用省to的不定式,

答案

首先要知道非谓语动词有三种形式
1 (to) do 有将来意味
2 doing 表主动
3 done 表被动
此句话中“fell into the river”掉进河里,暗含主动并非将来或被动而且别掉进河里也讲不同,看到的应该是正在发生的事也不能不过用将来时.