—How many students are there in the classroom?—_____ .I don’t know where they have gone.
---Where’s your father? ---He __________ to Singapore for a meeting. He ________ there twice.
He_____his computer last year. I _____ my computer for over ten years. It still works OK.
---Look at the boy running on the playground. Is it David? ---It ______ be him. I saw him go to the teachers’ office just now.
---How long __________ your parents ___________? ---For about twenty years.
The weather in Hong Kong is quite different from __________ in Beijing.