When passengers fly in an aircraft and remain seated without moving for extended periods, swelling can occur in their lower legs. Which statement accounts for this?
- AFewer leg muscle contractions occur to push blood along the veins.
- BThe rate of the heartbeat is reduced as no exercise is happening.
- CThere is little or no arterial blood pressure to force the blood upwards.
- DValves in the veins do not fill up with blood to prevent its backflow.