Part 4. Clean air cars.
Keywords.

natural gas, taxicabs, fossil fuel.
Vocabulary.

pollutant, carbon monoxide, fleet, entrepreneur, inaugural, dissipate, impact, combustible, fossil fuel, untapped, wean off, gas hose, Chevrolet Caprice, compressed natural gas (CNG).
A. Have a pre-listening discussion on the following three questions.
1. Besides gasoline or petrol, what can cars be powered by?
2. Have you ever heard about cars powered by natural gas? Do you know the advantages and disadvantages of using natural gas?
3. Do you think cars powered by natural gas will be a new trend of automobiles in the future, Why or Why not?