Answer: D. walking speed of 3 to 4 mph
Explanation: Moderate intensity physical activity has been generally described as an indulging physical activity which is capable of aiding an individual burn three to six times as much energy per minute as one does when sitting redundantly. From studies, a moderate intensity physical activity is characterized by maintaining a walking speed of three to four miles per hour which is equivalent ot burning off 3 kcal per kilogram per hour. This is different from the vigorous intensity physical activity which involves more strenuous requirements and ultimately leads to burning of more energy. Intensity physical exercises helps in fightinh and preventing obesity and other effects related to fat accumulation.