The Competitive Market Equilibrium Price of Sanitation Services in a Small

The competitive market equilibrium price of sanitation services in a small town with no government-supplied sanitation services is $2 per trash pickup. There is a $1 marginal external benefit associated with each trash pickup. The elasticity of supply of trash pickups is infinite in the long run, implying a horizontal supply curve. To achieve the efficient output of sanitation services,

A) a corrective subsidy must increase the price received by suppliers to $3 per pickup.
B) a corrective subsidy must decrease the price paid by consumers of sanitation services to $1 per pickup.
C) a corrective tax of $1 per pickup is required.
D) a corrective subsidy must increase the price paid by buyers to $3 per pickup.