—Listen! Is Mary singing in the next room?—No. It _______ be Mary．She has gone to Shanghai for an important meeting.

The boy insisted that he __________ nothing wrong and that he __________ at once.

I ______ follow you. Would you please repeat it?

(2013·江西六所重点高中一模)We ________ take clean drinking water for granted. One day we may run out of it.

According to common practice, the president _________ hold office for five years.