Correct Answer: (D) It is the number of calories needed to maintain body function at rest.

Step 1 - Meaning of BMR:

Basal Metabolic Rate is the minimum amount of energy the body needs to carry out its basic involuntary functions - breathing, blood circulation, heartbeat, cell repair and maintaining body temperature - while completely at rest.

Step 2 - The key word:

The word 'basal' means at the base level, that is, at complete rest and not during any activity.

Step 3 - Why the others are wrong:

Options (A), (B) and (C) all connect the calories to movement, exercise or high speed. Energy used during activity is over and above the BMR and is not part of it.

Note: BMR is affected by age, sex, body composition, hormones and climate.