—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?

The boy         the first prize, but he was so careless as to make a foolish mistake.

When a pencil is partly in a glass of water, it looks as if it ______.

(2013·高考天津卷)If he had spent more time practising speaking English before，he________ able to speak it much better now.

 Mr. Li, a man calling himself Smith wants to see you. ________ he come in?