Firm a and Firm B Emit 300 Tons of Pollution

Firm A and Firm B emit 300 tons of pollution each and each have marketable permits that allow each to emit 100 tons of pollution. If it costs $5,000 for Firm A to eliminate 100 tons of pollution and it costs Firm B $6,000 to eliminate 100 tons of pollution, then

A) Firm B sells its permits to Firm A for a price above $6,000.
B) Firm A sells its permits to Firm B for a price below $6,000.
C) Firm A sells its permits to Firm B for a price above $6,000.
D) Firm B sells its permits to Firm A for a price below $6,000.
E) neither Firm A nor Firm B sell permits because neither have extra permits.