Answer:
a. It is a competitive market: There are many colleges (hundreds). Students have options.
b. It is not a competitive market: The US Postal Service has exclusive right (monopoly).
c. It is not a competitive market. The market is an oligopolistic competition. The competition is limited by the few number of sellers.
d. It is a competitive market. There are many dozens of producers. The buyers have choices to make.
Step-by-step explanation:
In a purely competitive market, there are many sellers and many buyers. No seller or buyer dictates the price, supply, or demand. The market forces interact to achieve market equilibrium.