How much time did you __________ on the project?
Many people in the west make ________ a rule to buy Christmas presents for their relatives and friends.
Has ________ been decided when we are to hold the sports meeting?
The doctor kept telling him that he mustn’t smoke, but ________ didn’t help.
Don’t leave your keys in the car. Someone might steal ________ 。
Computers must be of great use to ________ doing the scientific research.