Which of the Following Best Explains Why Vasoconstrictors Are Effective

Which of the following best explains why vasoconstrictors are effective in increasing durations for local anesthesia?

A) Primary action on alpha receptors causes contraction of smooth muscles in blood vessels
B) Primary action on alpha and beta receptors causes contraction of smooth muscles in blood vessels
C) Primary action of beta receptors causes initial contraction of smooth muscles in blood vessels followed by vasodilation of blood vessels
D) Primary action on alpha receptors causes initial vasodilation of the smooth muscle