So far, all of the infected people are thought _______ the flu after direct contact with sick birds.

_________ I use your telephone?— Yes, of course.

Look! The light is still on. Is Mr Wu working in his office？—No, it _____ be Mr Wu. He has gone to Nanjing for a meeting.

We have to work for ________ to finish the work.

Go and ask Mr Green for help.—But I don’t know ______.