Due to the recent increase in the price of natural gas, the quantity of coal demanded by electric power generation plants has increased. Based on this information, coal and natural gas are:

A) complements.
B) substitutes.
C) independent goods.
D) none of the above

Substitutes

Goods or services that can replace each other in use, where an increase in the price of one leads to an increased demand for the other.

Natural Gas

A fossil fuel used as a source of energy for heating, cooking, and electricity generation, consisting mainly of methane.

Coal

A combustible black or brownish-black sedimentary rock, composed mostly of carbon and hydrocarbons, used as a fossil fuel.