The children are giving their classroom a good cleaning, ___ are sweeping; ___ are mopping. 

The field research will take Joan and Paul about five months; it will be a long time _________ we meet them again.

---I’m too busy, could you do _______ to help me?--- Of course. I can do _______ for you if you want me to.

We have been looking at houses, but haven’t found _____ we like yet.

 ----How do you like the book?----It’s quite different from ______ I read last month.