Local anesthetics rarely cause serious adverse effects. Which of the following is the best explanation for why?

a. The only organ sensitive to the sodium channel blocking effects of local anesthetics is the heart, but the heart is protected by the blood-heart barrier (BHB)
b. Due to the local routes of administration used for local anesthetics, the amount of drug that is absorbed into systemic circulation is limited
c. Local anesthetics are often rapidly metabolized in whatever tissue they are administered to
d. All local anesthetics have a very high therapeutic index