When should the taxi roof-sign give an “Available” signal?

1. Only during the winter and when there are passengers in the taxi.
2. Only during the day and when there are passengers in the taxi.
3. Only on holidays
4. Correct answer: Whenever there are no passengers in the taxi.

WhyThe taxi roof sign shows 'Available' whenever there are no passengers in the car. Seasons and holidays have nothing to do with it.