Question

asking the question \why is this true?\ is a good way to generate __________ for speeches on question of fact.
a. supporting materials
b. a thesis statement
c. main ideas
d. a conclusion

Explanation:

When building a speech about a question of fact, asking "Why is this true?" prompts you to gather evidence, data, and reasoning to back up the factual claim. This evidence constitutes the supporting materials that validate the core fact you are presenting. A thesis statement is the core claim itself, main ideas are the primary pillars of the speech, and a conclusion wraps up the speech, none of these are generated by this specific question.

Answer:

a. supporting materials