What precautions should you take to avoid carbon monoxide poisoning?

• Don't leave your vehicle engine running in a garage.
• Don't leave your vehicle engine, heater or air conditioner running in a parked car with windows closed.
• Don't drive with a defective muffler or exhaust system.
• All of the above.
  Explanation:

  "Simple precautions to avoid carbon monoxide are: 1. Don’t leave the car motor running in a garage. 2. Don’t leave the car motor running and the windows closed while the car is parked. 3. Don't operate the heater or air conditioner in a parked car with the windows closed. 4. Don't drive with a defective muffler or exhaust system."