I want to buy a bike. At last I decided ____ a black one.

Do you mind my smoking here—_________, Look at the sign. It says, “No Smoking.”

It can be easy to _______ such bad habits as smoking and heavy drinking, but it is not so easy to quit.

s population is expected toincrease to about 15 billion in 2040, _____ it will start to decline slowly

He will stop showing off, if no notice _________of him