—Look! Is that Mr. Green?—It          be Mr. Green. He has gone to Shanghai.

The first question was difficult, but the rest were pretty easy.

Teachers should ___them to continue studying when some students want to give it up. 

---I was told to be here at this time.---Sorry, you ___________. I forgot to tell you we've changed the plan. 

 —Must we finish the project in a month?—No, you _______.