--The research on the new bird flu virus vaccine is challenging and demanding. Who do you think can do the job? ---____ my students have a try?
It will make ______big difference if this experiment becomes ______ success.
By the time my mother came back from work, my sister and I ________ supper and were waiting for her at the table.
As is reported, it is 100 years______Qinghua University was founded.
He had his camera ready____ he saw something that would make a good picture.
They were busy ________ an experiment when I came.