Final answer:
A rental price ceiling of $600 a month has caused a shortage of student rental apartments. The most likely cause of this shortage is a decrease in the supply of student rental apartments.
Step-by-step explanation:
A rental price ceiling of $600 a month has been established, causing a shortage of student rental apartments. The most likely cause of this shortage is b) a decrease in the supply of student rental apartments. When the price ceiling is set at $600, suppliers are less willing to offer their apartments for rent due to reduced profitability, resulting in a decrease in the quantity of apartments available for rent and causing a shortage in the market.