What should we do to protect the fish in the river？
We_______ throw rubbish into the river．（ ）
| A． |
need |
B． |
needn't |
C． |
must |
D． |
mustn't |
Professor Tu Youyou never stops doing research on Chinese medicine，______？（ ）
| A． |
is she |
B． |
does she |
| C． |
isn't she |
D． |
doesn't she |
The two companies decided to work together ______ they had common interest．（ ）
| A． |
because |
B． |
unless |
C． |
but |
D． |
or |
______ I park my car here for a while？
No，you mustn't．Do you see the sign"NO PARKING"？（ ）
| A． |
Would |
B． |
May |
C． |
Must |
D． |
Should |
The workers are busy _______ windows to the new building these days．（ ）
| A． |
fix |
B． |
fixed |
C． |
fixing |
D． |
to fix |
Vivian refuses ______ her children to the weekend training centre for extra classes．（ ）
| A． |
to send |
B． |
sending |
C． |
sent |
D． |
sends |