In what types of buses is it obligatory to have a speed retarder?

1. Every bus in which a techograph was installed.
2. Correct answer: Buses with a minimum all up weight of 10,000 kg.
3. Every bus in which a retarder was installed during its manufacturing process.
4. Every bus that is permitted to carry more than 20 passengers.

WhyA speed retarder is required on buses with an all-up weight of at least 10,000 kg. The number of seats or a tachograph is not the criterion.