My parents will take me to Hong Kong ________ vacation.[ ]
Do you think necessary to do a bird count ?Yes , we must count them at least once a year
Mary __________ to school on foot every morning.
Do you know the man ________ visited the United States in February?–Yes. He is Chinese Vice-President Xi Jinping. He said it was his ____ visit to the United States.
Listen! Helen is singing in the classroom.—It _______ be Helen. She has gone to Shanghai.