Correct answer:

This comprises a network of veins lying deep to the deep fascia that envelopes the muscular compartments of the leg. Smaller tributaries drain into the popliteal vein behind the knee, which then ascends as the femoral vein to the inguinal ligament, where it becomes the external iliac vein. From there, blood passes up the common iliac vein, via the inferior vena cava, to the right atrium.