What should you do if a driver cannot complete a pass and needs to move back behind you?

• Speed up to create space for the vehicle to merge behind you
  Explanation:

  "If the passing car is at a point where the pass can be completed with your help, slow your speed to allow the driver to move ahead of you quickly. If it becomes clear that the driver cannot complete the pass and must drop back, increase your speed, leaving room for the vehicle to move in behind you again. "
• Slow down and let the driver try again
• Move to the shoulder to give more room
• Honk to signal the driver to stop