Which of the following options is the best reason to use presentation aids?
a they cover up a speakers visible nervousness
b they your audience understand and remember
c they can substitute for a general lack of information
d they can a speaker stay within the time limit

I believe your answer is B, they help your audience understand and remember. This will also help people who think mostly in images to understand your presentation.

Ibelieve this is the part where ulysses reveals his true identity to his faithful servants eumaeus and philaetius: his ragged vest then drawn aside disclosed the sign conspicuous, and the scar exposed: eager they view'd, with joy they stood amazed with tearful eyes o'er all their master gazed: these servants know ulysses by the scar he got when he was a child - so when he showed them the mark, they immediately knew this is truly their master and they hugged him, finally starting to believe his words.