What does your textbook advise regarding the use of hypothetical illustrations in a speech?

a. Using a series of hypothetical illustrations can often have more impact than a single illustration.
b. Make sure your audience knows from the beginning that your illustration is hypothetical.
c. A hypothetical illustration is only effective if it is lengthy; brief hypotheticals are ineffective.
d. Hypothetical illustrations are fine in a conclusion, but shouldn't be used in the body of a speech.

b