Regardless of the type of speech, it is important that your supporting materials are
a. humorous
b. credible
c. isolated from the main idea
d. all of the above

The alternative that best completes the sentence is the following one:

b. credible.

Explanation:

If you want to make a point, it is important that your supporting materials are solid so the ones listening to you give you credibility. In other words, your ideas and arguments must come from reliable sources so they appear to be credible or plausible.

if this is referring to star wars, han shot first.