---I can’t find my pen. ---___ you put it in your book.
--- Lin Tao, can I use your English dictionary? --- Sure. But you _______ return it before the class.
You_______ play with the knife. You ______ hurt yourself.
— It seems that Mr. Wu is standing there. — It ______ be him because he called me from Canada just now.
—Will you please answer the door? It ________ be your sister. —Sorry, I ________. I’m feeding the rabbit.
--- Listen! David is talking happily with his mother in the next room. --- It ______ be his mother. She has gone to Yunnan to be a volunteer doctor.