Why is proper ventilation and fresh air circulation management critical in passenger coach cabins during long-distance trips?

1. Continuous air circulation prevents carbon dioxide accumulation, reduces passenger motion sickness, and helps keep the driver alert
2. Ventilation is only necessary if the bus is carrying livestock in the passenger compartment
3. Fresh air intake causes the bus engine cooling fan to rotate in the wrong direction
4. Passenger bus windows must remain hermetically sealed without any air conditioning operation to save fuel