Great changes ________ in China since the People’s Republic of China _________ in 1949.

The boy was so ______ in reading that he didn’t hear his father knocking at the door.

Michael,do you go swimming?— Twice a week.

Listen! Is Mary playing the piano in the room? –No. It ________ be Mary. She has gone to Hong Kong.

Whose comic book is it?— It ________ be Daniel’s. He often shares his comic books with his friends.