In fact, ___is a hard job for the police to keep order in an important football match.
What do you think of the reason _____ he gave at the meeting yesterday?
Scientists say it may be five or six years ____ it is possible to test this medicine on human patients.
Every minute must be made full use of ____ our lessons, for the final examination is coming.
The foreigner does speak Chinese well, but of course not _____ we Chinese.
The reason _____ he refused to attend the meeting was that they didn’t give him an invitation earlier.