Which of the following can cause dangerous levels of CO to accumulate in or around a vehicle?

• Operating a vehicle with the trunk or rear tailgate open
• Operating a vehicle with holes in the body of the vehicle
• Operating a vehicle with a tailpipe that is blocked by debris, including snow, leaves or water
• All of the above
  Explanation:

  "Some conditions that can cause dangerous levels of CO to accumulate in or around a vehicle include: 1. Operating a vehicle with the trunk or rear tailgate open. 2.Operating a vehicle with holes in the body of the vehicle. 3. Operating a vehicle with a tailpipe that is blocked by debris, including snow, leaves or water."