He goes to school by bus, but __________ after school.

People have lots of problems living in the central Australian desert, ____ the lack of water is the most serious one.

Tom was about to close the window　　　　 his attention was caught by a bird.

____ you sing the English song?— Yes, I can.

Mom, I’m leaving. －It’s raining. You’d better ________ an umbrella with you.