Gasoline is what's called a nonrenewable source. That means, there's only so much to go around. It's already in the earth as oil, and when it's used up, there is no more. Coal, oil, natural gas, even the uranium needed to make nuclear power are nonrenewable sources. The fuel a sailboat uses is wind.
Wind is an example of a renewable source.
For example, as long as the sun shines, it will warm up whatever is placed in its path. That warmth can be turned into energy that can power everything from a calculator to a car. Gas, oil, and coal are called fossil fuels because they were created out of fossils millions of years ago. They need to be burned to produce energy and that burning causes air pollution. Between that and cars, it's no wonder our cities have such dirty air.