Which statement most accurately describes Coronary sinus?

A. The motor nerve to the diaphragm, arising mainly from cervical roots C3 to C5. B. The main venous channel that drains most of the myocardium into the right atrium. C. An arterial anastomotic ring at the base of the brain connecting anterior and posterior circulations. D. A vessel that carries nutrient-rich blood from the gastrointestinal tract to the liver.