Mel and Gibson Each Operate Petrol Stations Along the Great

Mel and Gibson each operate petrol stations along the Great Ocean Road in Victoria.They are the only petrol stations for hundreds of miles along the road.Which of the following agreements between them is most likely to substantially lessen competition?

A) An agreement to pool some money together to erect barriers along a particularly dangerous stretch of the road.
B) An agreement to buy coffee from the same supplier, Nescafe.
C) An agreement to sell motor oil at the same price.
D) An agreement to sell the same brand of muffins from their convenience stores.