—Mary’s score on the test is the highest in her class.—Really? She     have studied very hard.

---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?

Premier Wen advocated school bus safety_______.

_____there be a flood this summer, what would we do?

He insisted that the book _______ to the school library at once.