. ----______are they staying in Beijing?----For three days. 

-- Is air the lightest thing in the world?-- Not            . Scientists from Zhejiang University have just developed the world’s lightest material.

As a member of the Wild Animals Club, he ____ buys furs.

--- I feel so nervous before the exam that I can't sleep well at night. --- I think having a holiday will_______ help you relax.

—  What are you going to do this weekend?—  I’m not sure ______. Maybe I am going swimming.