Final answer:
The answer is a. Decreased hydrostatic pressure. The most common causes of edema formation are decreased plasma oncotic pressure, lymphatic obstruction, and sodium retention. Decreased hydrostatic pressure is not a common cause.
Step-by-step explanation:
Increased filtration of fluid from capillaries and lymph into surrounding tissues, leading to edema formation, can be caused by decreased hydrostatic pressure, decreased plasma oncotic pressure, lymphatic obstruction, or sodium retention.
However, decreased hydrostatic pressure is not a common cause of edema formation. Hydrostatic pressure is the pressure exerted by fluid in the capillaries, and a decrease in hydrostatic pressure would actually decrease the filtration of fluid into the surrounding tissues.