Final answer:
The most important variable concerning the communicator of a persuasive appeal is credibility, followed by attractiveness.
Step-by-step explanation:
The most important variable concerning the communicator of a persuasive appeal is credibility. Credibility refers to the speaker's expertise on the topic and their trustworthiness. Research has shown that speakers who are perceived as credible are more persuasive. While attractiveness can also influence persuasion, it is not as important as credibility. Therefore, the correct answer is e. both a and b only.