The main idea of this passage is ______.

A．The initial cost is very low.
B．The fuel costs are cheaper.
C．Wood fires are more efficient, cleaner, and safer than ever before.
D．The wood-burning stoves are more efficient than gas or oil ones.

A．many Americans have switched from hydrocarbon-based fuels to wood because the price of the latter has risen
B．some wood-burning stoves cost up to one hundred times more than others
C．catalytic combustors increase the amount of pollution caused by wood burning stoves
D．agitators are cheaper addition to wood-burning stoves than catalytic combustors