The correct option is A prepares the body for intense physical activity
Heartbeat can be regulated by the nervous system.
The sympathetic nervous system (SNS) prepares the body for intense physical activity (fight or flight). It increases the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output.
The parasympathetic nervous system (PSNS) relaxes the body and inhibits or slows many high energy functions. It decreases the rate of heart beat, speed of conduction of action potential and thereby the cardiac output.