The Underlying Reason Why Gasoline Prices at Neighboring Stations Is

The underlying reason why gasoline prices at neighboring stations is usually identical is that

A) collusion is legal in the energy sector.
B) collusion is prevalent in the energy sector.
C) because under oligopoly, it can be in each firms best interest to independently charge a price equal to their competition's price.
D) these operators are usually friends and benefit from the other's presence.