5. Passage Twenty-NineHow can we get rid of garbage (垃圾)? Do we have enough energy sources to meet our future energy needs? These are two important questions that many people are asking today.Some people think that man might be able to solve both problems at the same time.They suggest using garbage as an energy source， and at the same time it can save the land to hold garbage.For a long time， people buried garbage or dumped (倾倒)it on empty land.Now， empty land is scarce.But more and more garbage is produced each year.However， garbage can be a good fuel to use.The things in garbage do not look like coal， petroleum， or natural gas; but they are chemically similar to these fossil fuels.As we use up our fossil-fuel supplies， we might be able to use garbage as an energy source.Burning garbage is not a new idea.Some cities in Europe and the United States have been burning garbage for years.The heat that is produced by burning garbage is used to boil water.The steam that is produced is used to make electricity or to heat nearby buildings.In Paris， France， some power plants burn almost 2 million metric tons of the city’s garbage each year.The amount of energy produced is about the same as would be produced by burning almost a half million barrels of oil.Our fossil fuel supplies are limited.Burning garbage might be one kind of energy source that we can use to help meet our energy needs.This method could also reduce the amount of garbage piling up on the earth.The best title for the passage may be ().