The rivers will become dirtier and dirtier________ we take action to protect them.
—May I speak to Mr Wang, please?—Sorry, he is not in. Can I take a (an) _______ for you?
—Tom looks very sad. What’s wrong _______ him?—An accident happened _______ his father this morning.
The boy felt very _______ and fell _______ as soon as he lay on the bed.
This is _______ book I bought yesterday. Isn’t it ________ interesting one?
—We’ll study in different schools next term. Enjoy your time in the new school!— __________.