—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?

We were caught in the heavy traffic jam. Otherwise, we _____ on time.

I wrote a letter to John for his help during my high school years. without which I  the college entrance exam.

 “I heard they went skiing in the mountains last winter.” “It _________ true because there was little snow there.”

You _________ pay too much attention to your reading skill, as it is so important.