According to Article 55 of the Road Traffic Safety Law Implementation Regulations, what are the statutory rules for carrying a passenger on a regular two-wheeled motorcycle (普通二轮摩托车)?

1. A two-wheeled motorcycle may carry at most ONE passenger; children under 12 years of age are prohibited, and the passenger must sit facing forward straddling the rear seat wearing a certified helmet
2. A two-wheeled motorcycle may carry up to three adult passengers provided all share one helmet
3. Passengers may sit side-saddle with both legs on one side while holding luggage
4. Infants may be carried in a front backpack by the driver while riding