Skateboards International of Long Beach,California,was Able to Sell 20,000 Skateboards

Skateboards International of Long Beach,California,was able to sell 20,000 skateboards at a price of $60 in 2008.In 2009,it is able to sell only 12,000 of the same skateboards at a price of $60.Evidently,Skateboard International has experienced a(n) :

A) increase in quantity supplied.
B) increase in demand.
C) increase in supply.
D) decrease in demand.