The Bulges That Give the Lymphatic Vessels the "String of Beads

The bulges that give the lymphatic vessels the "string of beads" appearance are caused by

A) periodic inflammation of the tissues that remove bacteria and viruses from other body tissues.
B) closely spaced valves within the vessels.
C) thickenings in the endothelial lining of the lymph vessels at evenly spaced intervals.
D) regions of higher pressure within the lymph vessels, which cause the walls to bulge.
E) None of the answers are correct.