Science is really _______ useful sucject although it is very difficult.

Where can you find Li Hong—-Let me see. She is in _________. Her classroom is on the first floor.

He spoke at the meeting and said that three years in high school ________ not long[ ]

Air pollution is getting more and more serious，so we must take action________it is too late

Do you know ______ “s” in the word “advise” doesn’t make _______ /s/ sound．