Question

选择 （ ）someone knocket____the door while I____ my breakfast A.on;had B.at;were harving C.on;am

C.on;am having D.at;was having

Answer 1

D

敲门 know at the door 固定搭配
所以AC不对
主语I，单数，所以用was having
当有人敲门时，我正吃早饭。

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Answer 2

”knoked“？
一般如果knock用作动词时，用on,
如果knock用作名词时，用at.
没有太绝对的区别，只是一般这样使用
eg:
Did I hear a knock at the door?
Please do not enter before knocking on the door.
Ans:on, was having