B  

Nitrates primarily cause venodilation, which pools blood in systemic veins and lowers ventricular filling pressure, thereby reducing preload and myocardial oxygen demand—the key factor relieving anginal pain. Coronary dilation and afterload reduction occur only at higher doses and are less important acutely [Abrams, 1985, PMID 3925741; Tarkin & Kaski, 2016, PMID 27311574].