**Core Concept:** Atherosclerosis is a condition characterized by the formation of plaques in the arterial walls, causing reduced blood flow and potential organ ischemia. Coronary artery bypass graft (CABG) surgery involves using a healthy vessel to bypass the blocked coronary artery. A suitable vein for this purpose is the great saphenous vein (GSV), which runs along the medial aspect of the leg.

**Why the Correct Answer is Right:** The correct answer, option C, is the saphenous vein. This vein originates from the medial aspect of the leg, both above and below the knee, and eventually joins the femoral vein.

**Why Each Wrong Option is Incorrect:**

A. The popliteal vein (option A) is a smaller vein located in the popliteal fossa and does not extend from above the knee to below.
B. The anterior tibial vein (option B) is another vein in the leg, but it originates from the anterior aspect of the leg and does not join the femoral vein via the saphenous vein.
D. The plantar digital vein (option D) is a small vein in the sole of the foot and is unrelated to the saphenous vein system.

**Clinical Pearl:** The great saphenous vein (option C) is a reliable choice for CABG grafting due to its length, availability, and the fact that it avoids the risk of spasm or thrombosis associated with arterial grafts. It is essential for surgeons to identify and preserve the saphenous nerve during vein harvesting to minimize patient morbidity.