Choices:
I. activation energy;
II. ice;
III. electricity;
IV. snow;
V. glaciers;
VI. burning wood;
VII. Electrical energy;
VIII. Fuel cells;

Fact 1: Burning wood is used to produce heat. Fact 2: Heat is added and the temperature of the water increases. Given the two facts above, what is used to increase temperature?
Answer:
VI.