Most wine bottles are made of green, brown or clear______.

______ is a person who studies the natural relationships between the air, land, water, animals, an plants.

Car ______ is the main reason for the city's pollution.

The sun, water and the wind are other______ sources of energy.

Solar panels are used to_______ satellites.

We should try to make_______ of the facilities we have already had.

We need to cut down on our fuel_______ by having fewer cars on the road.

Water power______ energy without pollution.

Air______ is caused by many reasons like heating coal, using so many cars.

The dam______ back the water suddenly gave way.