A Category B car tows a trailer with maximum authorised mass over 750 kg. Under HAK's category table, when can this still be within Category B without moving to BE?

1. Only if the combination's maximum authorised mass is not more than 4,250 kg, with an additional driving exam required when the combination exceeds 3,500 kg
2. Always, because Category B has no trailer combination limit
3. Only when the trailer is empty, regardless of authorised mass
4. Only on roads outside built-up areas