What is the decisive factor in future competition between nations

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．Wood-bunting stoves are safer and more efficient than they used to be.
B．No factories exist for the purpose of producing dirty wood chips.
C．Both catalytic combustors and wood agitators save money in the long run.
D．Wood-burning stoves with catalytic combustors cost between $ 100 and $ 200.