Which vessel drains most of the coronary veins and empties directly into the right atrium?

1. The right atrium receives blood from three main sources. 2. The superior and inferior venae cavae drain systemic venous blood from above and below the diaphragm respectively. 3. The coronary sinus, a thin-walled vessel, drains most of the coronary veins that return blood from the heart itself and also empties into the right atrium. 4. The pulmonary trunk carries blood away from the right ventricle rather than draining coronary veins, so it does not match this description. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 19 "The Cardiovascular System: The Heart", section 19.1, p. 835_