Answer:
A sociologist would describe Ezra Klein as a:
d. opinion leader.
Step-by-step explanation:
According to the passage, Ezra Klein was able to influence Caleb's opinions informally. With time, Caleb has started to think more and more like Klein. This is described in sociology by the term opinion leadership. An opinion leader is someone who is capable of influencing and persuading others to think and act in a way that is in accordance to his own opinions and preferences.