—— Hurry up. The bus is coming! —— Oh, no, we mustn’t cross the street ______ the traffic lights are green.
—Do you know___? —He is a dentist.
—Excuse me, could you tell me where_____? — Sure, sir. You can try
— I don't know______. — Because he has to look after his mother.
— Could you tell us how long ___? — About three days.
— I don’t know next. — Let’s ask our teacher for help.what to do B. what should I do C. how to do D. how I should do