Answer: B
Explanation: The other answers are talking about similarities among different species.
Heart rate is controlled by the two branches of the autonomic (involuntary) nervous system. The sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). The sympathetic nervous system (SNS) releases the hormones (catecholamines - epinephrine and norepinephrine) to accelerate the heart rate.
A food chain can usually sustain no more than six energy transfers before all the energy is used up. And so less energy is transferred at each level of the food chain so the biomass gets smaller.
The correct answer is D: stable and not growing or shrinking. I hope this helped:)