Which of the following kinds of professionals is most likely to be held to a nationwide standard of care for professionals in their field?

a. A general practitioner lawyer in a very small town.
b. A general practitioner physician in one of the largest cities in America.
c. A certified brain surgeon (i.e., a physician who is board certified in the specialty of brain surgery) regardless whether practicing in a large city or a small town.
d. A general practitioner dentist.