__________at the door before you enter the office，or you’ll be considered impolite
#65893
A
Knocking
B
Knocked
C
Knock
D
To knock
推荐题目
It’s really not ___________ you to do such a silly thing.
#59424
A
clever enough of
B
clever enough for
C
enough clever for
D
enough clever of
---Andy, _________, it’s time to have breakfast. ---OK, mum.
#59387
A
get up
B
gets up
C
getting up
D
to get up
Everything is full of yellow dust because of the sandstorm（沙尘暴）. ！
#66115
A
What terrible a weather
B
What terrible weather
C
How terrible a weather
D
What a terrible weather