How are visual aids used most effectively in a speech?
a. to support a speaker's point by providing evidence or clarity
b. to provide additional information that the speaker doesn't mention
c. to cite the sources of the information that the speaker is using
d. to establish credibility for the speaker by using quotations

The additional information that the visual material can provide comes to support the speach for a better understanding ( to reach the audience more effectively depending on the structure of the audience cause man- for example- have the tendency to remember better what they see rather then what they hear

it provides a unique and personal perspective on a significant historical event.

i think ur answer is c   hope this