Answer:
The correct answer is:
e. a and b only.
Using evidence in a persuasive speech can increase the speaker's credibility (a) and inoculate listeners against counter persuasion (b). While evidence can enhance the speaker's credibility and make the argument more persuasive, it might not necessarily compensate for fallacious reasoning in all cases.
NOTE: This answer may be wrong since I do not have the textbook.
:)