Final answer:
Females have lower cardiac outputs than males primarily due to a lower stroke volume, related to smaller heart and body size, not to higher blood viscosity, greater heart rate variability, or enhanced venous return.
Step-by-step explanation:
Females typically have lower cardiac output compared to males due to a variety of factors aside from muscular difference. One key factor is lower stroke volume (B). Stroke volume is the amount of blood ejected by the ventricles with each heartbeat. It is influenced by myocardial contractility, preload (amount of ventricular filling), and afterload (resistance faced by the left ventricle). Since females generally have smaller body size and heart size, they tend to have a lower stroke volume, which contributes to a lesser cardiac output compared to males. This is not associated with higher blood viscosity, greater heart rate variability, or enhanced venous return, which are not directly responsible for the observed gender differences in cardiac output.