Cai Qin has given concerts all over China and the tickets have always_______.

.It was obviously that the man ______ driving on the free way for almost an hour when he ______ that he must come back.

Look, your sister is playing the piano over there.－She ______ be my sister. She has gone to America.

Linda _____ many places of interest in China, and she still wants to go to more places.

_______ do you help your mother clean the house? —Once a week. [ ]