The correct answer is A. Dog.
The metabolic rate is the rate at which an organism consumes energy. It is usually measured in units of oxygen consumption per unit of body mass per unit of time. The metabolic rate of an organism is affected by a number of factors, including its size, activity level, and environmental temperature.
Dogs have a relatively low metabolic rate compared to other mammals. This is because they are relatively small animals and they do not need to expend a lot of energy to maintain their body temperature. Dogs also tend to be less active than other mammals, which further contributes to their low metabolic rate.
Elephants, horses, and humans all have a higher metabolic rate than dogs. This is because they are larger animals and they need to expend more energy to maintain their body temperature. Elephants and horses are also more active than dogs, which further contributes to their higher metabolic rate.
In conclusion, the correct answer to the question “Which amongst the following has the lowest metabolic rate of oxygen consumption (mm3/g hour)?” is A. Dog.