VEHICLES ALSO ACCOUNT FOR AIR…….…..(1) IN THE CITIES. AUTOMOBILE EX...

4. Vehicles also account for air…….…..(1) in the cities. Automobile exhaust and some industrial processes……..(2)

carbon monoxide, an odorless gas which can not be seen or………(3) nitric oxide is another tail-pipe emission……….

(4) is highly poisonous and may sometimes change into even more……..(5) nitrogen dioxide.