Question

Before returning to your original lane after passing another vehicle, you should: Beep your horn. See both headlights of the passed vehicle in your rearview mirror. Flash your headlights.

Answer 1

See both headlights of the passed vehicle in your rearview mirror.

Step-by-step explanation:

This is to ensure you as the driver have enough clearance before merging back into their lane.

If you are able to see both headlights of the passed vehicle in your rearview mirror, it means you are likely far enough out in front of them that you will not hit them when merging back into their lane.