Помогите с заданием по английскому

Pollution is the introduction of (1) harmful materials into the environment. These materials are called (2) pollutants. They can be natural, such as (3) volcanic ash or created by human (4) activity, such as trash or runoff produced by factories. All these materials damage the quality of air, water, and land.

Pollution is a (5) global problem. Urban areas are (6) usually more polluted than the countryside. Although it may seem (7) impossible, pollution can spread to remote places where no people live. Annually the level of pollution tends to (8) increase.

Here is the completed text with the appropriate forms of the words in brackets:

Pollution is the introduction of (1) **harmful** materials into the environment. These materials are called (2) **pollutants**. They can be natural, such as (3) **volcanic** ash or created by human (4) **activity**, such as trash or runoff produced by factories. All these materials damage the quality of air, water, and land.
Pollution is a (5) **global** problem. Urban areas are (6) **usually** more polluted than the countryside. Although it may seem (7) **impossible**, pollution can spread to remote places where no people live. Annually the level of pollution tends to (8) **increase**.

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