Which of the Following Best Explains the Drop in Blood

Which of the following best explains the drop in blood pressure that occurs when one goes from lying down to standing up?

A) The heart rate decreases. This is due to the baroreceptor reflex reducing sympathetic output to the SA node.
B) An increase in afterload causes a drop in stroke volume, cardiac output, and blood pressure.
C) An increase in preload causes a drop in stroke volume, cardiac output, and blood pressure.
D) Venous compliance allows blood to pool in the legs, decreasing venous return. This causes a drop in cardiac output and blood pressure.