(1)___ more and more countries become industrialized, there will be more and more competition for petroleum for cars, home heating, and industry. While (2) ____ petroleum contributes greatly (3) ____ acid rain, it is less (4) ____ than coal. Unfortunately, petroleum is more expensive than coal and the supply of petroleum will eventually run out. Therefore, there will be more and more pressure to burn coal for energy. Coal is a (5) _____ dirtier energy source than petroleum. Since we already know how destructive acid rain is, it is very important that we increase our efforts to find a non – polluting source of energy as quickly as possible so that we can avoid further environmental damage.