—It's no easy task to catch a ticket on a website that receives 1 billion clicks daily.—I can't agree with you more. There ________ be errors for every single step.

—Isn’t that Ann’s husband over there? ---No, it _______be him. I’m sure he doesn’t wear glasses.

----Whose is that book? ----It _________ belong to Lucy. Her name is on it.

--- 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 used to work in the same office and we____ often have coffee together, which I missed so much years later.