The demand for gasoline in a country is given by QD = 15 - 2p and the supply by QS = 3p, where the price is in dollars per gallon. The negative externality associated with carbon is $2 per gallon. In an unregulated market for gasoline, the deadweight loss associated with the externality is:

a. 2

b. 1.2

c. 0

d. 2.4