In an ideal situation that prices are regulated by the government, so the firms' decision is to choose their locations. Suppose there are two firms simultaneously choose their location in a linear city characterized by a unit interval [0, 1]. Which of the following statement is correct.

• Any location pair that both firms in the same spot is an equilibrium.
• There are no equilibrium. Both firms always trying to locate them differently from their opponents.
• Since prices are regulated, the location does not matter, so any location is the same.
• In the equilibrium, both firms choose to location in the mid-point.