Under national taxi operational service regulations, what is the rule regarding the use of air conditioning or heating inside the taxi cabin?

1. Drivers must turn on the air conditioner or heater upon passenger request at no additional charge
2. Drivers may charge an extra cash air-conditioning fee of RMB 5 per trip
3. Air conditioning is only allowed if the outside temperature exceeds 38°C
4. The driver has absolute unilateral discretion to keep windows down and refuse air conditioning to conserve fuel