Use the verbs in the brackets in the passive form.

1. Each year, large amounts of carbon monoxide (expel) into the air by automobiles and factories.
2. The weight of the planets (calculate) by Newton as a young man.
3. Water (discover) under the Sahara Desert.
4. Coal (produce) by plant matter of prehistoric times.
5. Soap (manufacture) by boiling vegetable or animal fat with sodium or potassium hydroxide.
6. Human speech (control) by a part of the brain called the cerebrum.
7. The hydrogen bomb (call) a thermonuclear bomb because extremely high temperatures (need) to start the fusion process.
8. Gold (not to affect) by moisture.
9. The engine is usually referred to as an internal combustion engine because fuel (burn) within its cylinders or combustion chambers.
10. The equipment (deliver) by truck.
11. A wind generator (power) by wind.
12. Water commonly (purify) by distilling it