What should you do if a vehicle you are passing speeds up?

• You should also speed up to complete your passing safely
• You should sound a horn.
• You should move back to your original lane without passing
  Explanation:

  "You should move back to your original lane without passing. If the vehicle you're passing speeds up, don't race. Safely return to your lane. It’s both unlawful and dangerous to speed up when another driver is trying to pass."
• You should downshift your vehicle.