How should you look behind when reversing your vehicle in a straight line?

• Look over your left shoulder through the rear window.
• Look over your right shoulder through the rear window.
  Explanation:

  "When reversing in a straight line, look over your right shoulder through the rear window for the best visibility. This allows you to see directly behind your vehicle and spot any obstacles or hazards."
• Look through the right side rearview mirror.
• Look through the left side rearview mirror.