You should do more .Don’t always sit at the desk doing your .A. exercise, exercisesB. exercises, exerciseC. exercises, exercises
We brush our teeth twice a day.
My mother is ill. I ______ stay at home to take care of her.
—Is Mr. Smith over there? —It ________ be him. He has gone to Beijing on business.
After a long walk, the old man be tired now.
You ________ worry about him. He will get well soon. A. needn’t B. can’t C. mustn’t