WHEN I WAS READING I HEARD SOMEONE -----(KNOCK)AT THE DOOR

题目

WHEN I WAS READING I HEARD SOMEONE -----(KNOCK)AT THE DOOR
为什么WHEN后加ING
不是在I HEAR后加吗/
告诉我规律
括号里的也要填!
谢谢!

答案

WHEN I WAS READING I HEARD SOMEONE who was knocking AT THE DOOR
等于WHEN I WAS READING I HEARD SOMEONE being knocking AT THE DOOR
自己看语法书吧,别纠缠语法,理解就行