Read the text and fill in the gaps with the correct form of verbs as per subject and context: 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) — (suffer) a lot.