Something must be done to prevent our city ____ by thick smoke.
— Is the man our sales-manager? — No, it ______ not be him he never plays cards.
For quite _____ students,their teacher's advice is more important than _____ of their parents'.
He was born ____ a very cold night _____ December.
When he knocked at the door, my mother was busy ____ supper.
He waited until it was dark ____ nobody could see him clearly.