---The research on the new flu virus vaccine is challenging and demanding. Who do you think can do the job? ---____ my students have a try?
I walked up to the top of the hill with my friends, ___ we enjoyed a splendid view of the lake.
The prize will go to the writer ___ story shows the most imagination.
It is one thing to enjoy listening good music. But it is ___ another to play it well yourself.
They ___ have arrived at lunchtime but their flight was delayed.
The next thing he saw was smoke ___ from behind the house.