—_________ I borrow your history book?—Sure. Here you are.

--- 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.

You _______be hungry already—you had lunch only two hours ago.

----- Where is Jack?.-----He______ be in the reading room .I saw him just now.

--- I spent two weeks in London last summer. --- Then you must have visited the British Museum during your stay, _______ you?