All of Martin's Friends Recognize That He Knows a Lot

All of Martin's friends recognize that he knows a lot about cars. He is very up-to-date on new models and knows about the performance and reliability of almost every car. His friends often ask Martin for his guidance when they are in the market for a new car. Martin can be considered a(n) _________ in regard to automobiles.

A) opinion leader
B) action leader
C) category influencer
D) decision guider