15. Which of the following statements concerning control of blood flow through arterioles is true? (A) Beta-adrenergic receptors are more abundant on most arteriolar smooth muscle than are alpha-adrenergic receptors. (B) If the arterial blood pressure to an organ suddenly decreases, arterioles in the organ will dilate in response. (C) Binding of epinephrine to alpha-adrenergic receptors causes vasodilation. (D) Increased stimulation of vascular smooth muscle by the parasympathetic nervous system causes increased vasoconstriction.