Which of these is most likely to lead directly to a black market?
a. a supply shock
c. rationing
b. a price floor
d. equilibrium

c. rationing

Explanation:

allow each person to have only a fixed amount of (a particular commodity).

i guess that visual aids present persuasive examples to what you are presenting, some factors would be theme (does it fit with the color, information, what you are presenting), size (can you see it, is it a big enough span of data/information), and overall look of the visual aid.

hope this : )