--- This must be a footprint of a tiger. --- It ____ be. A tiger’s should be much larger and deeper than this. 

Some people          feel sick when they read a book in a car or on a boat．

You _______ write the poem down. Our teacher will give us a copy. 

---Who is the tallest boy?      ---It ______ be John.. John is of medium height.

—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.