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
B:Knocked
C:Knock
D:To knock
正确答案是:
同类题型
I do not think jogging _____ me very much
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Do you want to play another game of cards — I’d like to, but it’s getting late. I really ______ go.
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