—What areyou busy with — We are carrying out a research ____ thecauses of cancer.

I wish you’d do ______ talking and some more work. Thus things will become better.

Mum, I’d love to go to Australia for this summer holiday.— But I doubt if we could ________ something like that.

______ is known to us all that 2012 Olympic Games will take place in Britain．[ ]

My Old Classmate also mentioned some important events that _______ from 1993 to 2013.