Final answer:
The body uses approximately 4.78 Calories for each liter of oxygen consumed, which rounds to 5 calories (option B) as the closest answer given the options provided.
Step-by-step explanation:
The body uses a significant amount of calories for each liter of oxygen consumed. The calculation of caloric value can be done using an indirect method, where calories are determined by the amount of oxygen used in the oxidation of nutrients. This is known as 'indirect calorimetry'. According to the materials provided, approximately 20 kJ of energy are produced for each liter of oxygen consumed, which is constant regardless of the type of food.
Since there are 4.184 kilojoules in one Calorie (also known as a kilocalorie), then 20 kJ corresponds to roughly 20 / 4.184 = 4.78 Calories. Therefore, for the sake of simplicity and given the options provided, the closest answer to how many calories the body uses per liter of consumed oxygen would be 5 calories (Option B).