__________at the door before you enter the office，or you’ll be considered impolite
| A．Knocking | B．Knocked | C．Knock | D．To knock |
The question _____ at tomorrow’s meeting is of great importance.
| A．to discuss | B．being discussed | C．discussed | D．to be discussed |
Not until she arrived home _____ that her wallet had been stolen.
| A．did she find | B．she found | C．would she fi nd |
D．that she found |
—Hi, Tom, Any idea where Jane is?
— She __ in the classroom. I saw her there just now.
| A．shall be | B．should have been | C．must be | D．might have been |
He’s got himself into a dangerous situation _____ he is likely to lose control over the plane.
| A．which | B．that | C．where | D．why |
Great changes ____________ in my hometown in the past few years.
A have taken place. B. took place C. have been happened D. were taken place