To keep the air fresh during the night, I often sleep with the windows on ________ it’s really cold.
Computers have made a great difference _______ our everyday life.
After half a day’s hard work, we made our classroom look as _______ as new.
_______ provides many hours of air for astronauts in space.
We are wondering ________ we can prevent people from polluting the earth.
The gravity on Mars is only about ________ of that on Earth.