1 . Their plan__________(approve); otherwise they wouldn’t have begun their work.

2 . 用适当的情态动词填空
（1）—Excuse me. Is this the right way to the Summer Palace?
—Sorry, I'm not sure. But it ____________be.
（2）—Do you know where David is? I couldn't find him anywhere.
—Well, he ____________have gone far - his coat's still here.
（3）Mr. Bush is on time for everything. How ____________it be that he was late for the important meeting?
（4）He ____________ have completed his work; otherwise,he wouldn't be enjoying himself by the seaside.
（5）Look!The light in the office is still on. Our English teacher ____________be correcting our exam papers.