People are _________the use of alternative energy sources. Because the fossil fuels _________will be used sooner or later.
When you ______ the book please return it to the library on time.
——You look so worn-out!——I lay ________ all the night.
Joe: Why don't you tell me a few things about your country? Ken: __________
With her long beautiful hair gone _______ would be no use for the combs.
The higher the birds flew, _______ we could see them.