——Why did Tan become interested in the sounds of nature?——__________he thinks the best music comes from nature.
The windows after school is over.
The factory has been closed a year ago.
There_____ a hospital in my hometown fifty years ago.
---Mum, may I go out to play football this afternoon? ---You can if your homework .
---Now the air in our hometown is even than it was before. ---So we must do something to stop it.