Question

he saw it ___when he was walking past A happening B happen

为啥是第二个呢

Answer 1

答案：A
解释：
1、see sb. do sth. 表示“看见某人做了某事”，用动词原形表示动作已经完成，强调是动作的全过程。比如：
I saw him get on the bus.
我看见他上了车了。
I saw him work in the garden yesterday.
昨天我看见他在花园里干活了。
2、see sb. doing sth. 表示“看见某人正在做某事”，用动词ing形式强调动作正在进行，比如：
I saw them playing basketball at 5 p.m. yesterday.
昨天下午五点，我看见他们在打篮球。
3、He saw it ___when he was walking past. 此句中“when he was walking past”意为“当他路过的时候”，也就是说当他路过的这个时刻，【发生】这一动作正在进行，所以用ing形式更为恰当。
4、综上所述，正确答案是A。

Answer 2

B