——The research on the new bird flu virus vaccine is challenging and demanding. Who do you think can do the job? ——____ Tom have a try?
It was really very dangerous. One more step, ______ the baby would have fallen into the well.
It is usually warm in my hometown in March, but it ________be rather cold sometimes.
No one had told Smith about __________ a lecture the following day.
If the food tastes nice, we will buy some; if ________, ________.
The man was charged ____________ the crime of betraying his country and sentenced ________ ten years in prison.