Consider the Supply and Demand Curves Depicted in the Diagram

Consider the supply and demand curves depicted in the diagram above. If the government imposed a price ceiling of $15, then sellers will be willing to sell ___, and a black market could develop where the price would be:

A) 24 units; below $15
B) 36 units; above $15
C) 24 units; above $15
D) 36 units; below $15