Why Does It Makes Sense That Metabolism Is Measured in Calories

Why does it makes sense that metabolism is measured in calories?

A) If your metabolism is slow you tend to gain weight, so it makes sense to tie it to caloric intake.
B) The chemical reactions of metabolism produce heat energy, and energy is measured in Calories.
C) If you are very active you burn a lot of Calories, so it makes sense to measure metabolism that way.
D) The more Calories you consume, the higher your metabolism will be.
E) Metabolic rate is determined by calorie consumption.