Refer to the Following Graph

Multiple Choice

Refer to the following graph. In New York City, the rent on many apartments is set below market rates. As a result, many people find that the only way to obtain an apartment is to make illegal payments to landlords. If Pc is the controlled rent, a best estimate of such "key" money is shown as:

A) Pf.
B) Pe.
C) Pe minus Pc.
D) Pf minus Pc.