Which of the following statements are true of coronary artery anatomy? A. Right bundle branch block in acute anterior myocardial infarction suggests obstruction prior to the first septal branch of the left anterior descending coronary artery B. the posterior descending artery is usually a branch of the circumflex artery C. The sinus node is supplied by a branch of the right coronary in over 90% of subjects. D. The AV node is supplied by the left anterior descending coronary artery. E. The left main stem is about 4 cm long