What Mechanisms Assist Venous Return

What mechanisms assist venous return?

A) One-way valves, increasing diameter of veins, peripheral resistance
B) Pressure changes during breathing, one-way valves, thickness of the tunica media in medium-sized veins
C) Skeletal muscle contractions, large-diameter lumen, thickness of the tunica media in medium-sized veins
D) One-way valves, skeletal muscle contractions, pressure changes during breathing