下列各句中，加横线的词语运用正确的一项是

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 was ________I got home two hours later ________I realized I’d left my most important textbook behind.

A growing number of people are beginning to believe that learning new skills and knowledge _________ more promotion opportunities.

In fact, more and more people ____ to live a greener, healthier and more environmentally “green life”