__________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 is to have a swim in a pool on a hot summer.
#65877
A
How fun
B
How funny
C
What fun
D
What funny
_____ through this book and tell me what you think of it.
#66199
A
Look
B
Looking
C
To look
D
Having looked
_______it is to jump out of an airplane at 10,000 feet!
#66146
A
What an exciting experience
B
How exciting experience
C
How an exciting experience
D
What exciting experience