Air (a) — (be) an important element of the environment. But it is constantly being (b) — (pollute) in many ways. We make fire to cook food and (c) — (do) many works. This fire emits smoke which (d) — (contaminate) air. Vehicles pollute air to a great extent by (e) — (burn) fuel Air pollution also (f) — (happen) when coal and oil (g) — (burn). Mills and factories can be (h) — (hold) responsible for this pollution. It is high time we (i) — (check) air pollution Otherwise we (j)