What does the courtesy rule allow at an intersection?

• It allows the vehicle that arrived first to proceed first
  Explanation:

  "The courtesy rule at an intersection suggests that the vehicle that arrives first has the right of way and can proceed first, as long as it is safe to do so and doesn't conflict with other traffic or pedestrians."
• It allows the vehicle that arrived last to proceed first.
• It allows vehicles to move at the same time.
• None of the above