When you approach a vehicle towing a trailer:

• Watch for any sway or possible hazards, such as crosswinds or slippery curves.
• Be aware that sudden braking might cause the trailer to jackknife.
• Use extreme caution while passing a trailer and the towing vehicle.
• All of the above.
  Explanation:

  "When you approach a vehicle towing a trailer: 1. Watch for any sway or possible hazards, such as crosswinds or slippery curves. 2. Be aware that sudden braking might cause the trailer to jackknife. 3. Use extreme caution while passing a trailer and the towing vehicle."