A Sure Sign of the Existence of an Underground Market

A sure sign of the existence of an underground market for rent-controlled apartments in New York City is that

A) rents are high.
B) apartment dealers work alongside drug dealers on its city streets.
C) though 60% of the city's apartments are rent-controlled only 3% of the apartment ads in newspaper are for rent-controlled apartments.
D) an open bribe must be paid to the mayor to get a rent controlled apartment.