Suppose that the average equilibrium monthly rental price of apartments and rooms in a college town had been steady at $600, but then the college expanded enrollment from 10,000 to 12,000, and suddenly there was a shortage of rental housing at the prevailing price of $600 . Which of the following is most likely to be true?

a. The shortage occurred because supply increased, and a new market equilibrium will feature lower rental prices and fewer rental units available on the market.
b. The shortage occurred because demand increased, and a new market equilibrium will feature higher rental prices and fewer rental units available on the market.
c. The shortage occurred because demand decreased, and a new market equilibrium will feature lower rental prices and fewer rental units available on the market.
d. The shortage occurred because demand increased, and a new market equilibrium will feature higher rental prices and more rental units available on the market.

d