All of the following are presented in your textbook as guidelines for ethical speechmaking except:. a. be honest in what you say.
b. avoid name calling and other forms of abusive language.
c. be fully prepared for each speech.
d. make sure your goals are ethically sound.
e. explain your credibility on the speech topic.

The ethical speechmaking is the use of the original speech content for deriving out the facts and giving appropriate attributes to the sentences.

Hence the option E is correct.

Learn more about the presented in your textbook as guidelines.

link.

e. explain your credibility on the speech topic.

Explanation:

There are clear guidelines written down in the textbook for ethical speechmaking such as being trustworthy, being respectful towards others, having dignified conduct, being honest in the message being passed across, and being an authority on the subject but not explaining your credibility on the speech topic.

When making a speech, it would be illogical and counter-productive to start to explain one's credibility on the speech topic, rather show you're an authority when you start your speech.