问题

__________at the door before you enter the office，or you’ll be considered impolite

A:Knocking
B:Knocked
C:Knock
D:To knock;

正确答案是：

同类题型

He is old, so his son will _________ the farm.

It doesn’t matter to us _______ you do.

In the evening I often talk _______ my friends _______ the Internet.

I ____ to send him a telegram to congratulate him on his marriage, but I ____ it

Our English teacher has a _____ teaching method