What Factors Are Involved in the Formation of Varicose Veins

What factors are involved in the formation of varicose veins?

A) Varicose veins form when blood pressure is too high damaging the valves.
B) Varicose veins form when blood pressure is too low so the valves do not open.
C) Varicose veins form when the vein walls weaken and the valves fail so blood begins to pool in the veins.
D) Varicose veins form when the valves become stiff and fail to open.
E) Varicose veins form when sympathetic activation causes venoconstriction.