If you are not sure you have enough distance to overtake a vehicle ahead, you should:

• A. Sound your horn to signal the driver ahead to slow down.
• B. Wait for a better opportunity with more distance to overtake.
  Explanation:

  "Always be sure that you have enough time and distance to complete your overtaking move. If you are not certain, wait for a better opportunity."
• C. Put the vehicle in a lower gear and speed up.