How Is Blood Pressure Maintained in Veins to Counter the Force

How is blood pressure maintained in veins to counter the force of gravity?

A) Blood pressure is maintained in veins because the heart pumps blood through the veins.
B) Blood pressure is maintained in veins because the valves reduce the flow of blood as blood passes by.
C) Blood pressure is maintained in veins by the contractions of surrounding skeletal muscles that squeeze venous blood toward the heart and the presence of valves which prevent backflow of the blood.
D) Blood pressure is maintained in veins by using the valves as pumps to push blood back toward the heart.
E) Blood pressure is maintained in veins by contractions of the smooth muscle in the walls of the veins that squeeze venous blood toward the heart and the presence of valves which prevent backflow of the blood.