Ex. 17. Change Active constructions into Passive ones.

Model: Some scientists estimate the number of plants and animals as three million.

The number of plants and animals is estimated as three million.

1. Some scientists estimate the number of plants and animals as three million. 2. Many of the plants provide us with food, clothing, shelter and medicines. 3. Some plants and animals can pierce our skin. 4. Certain plants and animals may cause diseases. 5. Scientists study living things with great care. 6. We have learned much about all the living around us.