We should try to prevent air pollution__________.

We don’t permit________in our school.Would you please put your cigarette out?—Forgive me. I didn’t know.[ ]

ly I was an observer at _____ parenteducation seminar about the depression, suicide, and anxiety disordersaffecting _____ children.

She ______ behind the door in order not to be found. Two minutes later she was safe again.

The father as well as the three children______ every Sunday afternoon in winter.