—A number of students________in the dining hall．
—Let me count．The number of the students________about 400．
A．are；is
B．is；are
C．are；are
We are very proud of these national________(英雄)．
She put back the book she had taken________mistake．
A．in
B．up
C．to
D．by
________it rains heavily，they go on working outside．
A．How
B．Why
C．Although
D．What
What________is the most helpful invention？
A．you think
B．I think
C．you do think
D．do you think
The dinner didn’t start________all the friends arrived．
A．since
B．until
C．while
D．by
