—Someone is knocking at the door. Who ______ it be? —It ______ be Tom. He is still in the school.
Kate and I _______ doing ________ homework now.
Do you have __________ to do?
--Tom has been to Beijing before. --________________.
Song Zuying’s ________ is sweet.
--____ do you send e-mails to your friends? -- Twice a week.