To live a low-carbon life , we must try to save _____ energy and produce ____ carbon .

---Some foreigners will visit our school tomorrow.---Great! It’s ______to tide up our school now.

--- ________ are your grandparents?--- They’re very well.

 Now China has joined WTO（世贸组织）, so I think English is________ useful than before.

 ---Which is ______, the sun, the moon or the earth?   ---Of course the sun is.