We should spend more time _______ schoolwork to get good grades.

_____ stiff after sitting so long,and could hardly walk

It is becoming more and more difficult to ____ the problems of traffic in some big cities of our country.

The report noted that nicotine breathed inby a smoker increased the need of the heart ________ oxygen

How many students do you think will be present at the meeting—I expect ______ 20 students at the meeting.