Answer:
The correct answer is letter "D": illegal.
Step-by-step explanation:
Blockbusting is the illegal practice by which real estate brokers spread the word among homeowners of a given area that the price of their properties is undervalued because of any false reason made up by the broker in an attempt of having owners to sell their houses so the broker can have more listings.
As a result of blockbusting, the price of houses decline. The license of brokers engaged in this activity is subject to disciplinary action.