We need a new leader for our Helping HandsClub, but I don’t know ______. — Why not Mary She is always willing to helpothers.

Forty percent of the class _______ most of the work, and some of the work ______ really difficult.

The scientists are now trying to discover what use can be ____such a material ____ the problem.

Better _____ all the lights are turned offbefore you leave the classroom．

Are you glad that you came to Changsha—Yes，indeed I going to Shanghai or Shenzhen，but I’ve never regretted my decision