If a carrier refuses to transport a PRM passenger alone because safety rules require an accompanying assistant, what is the carrier's obligation under Article 10(4) of Regulation (EU) No 181/2011 regarding the accompanying person?

1. The accompanying person must pay triple the regular ticket price
2. The accompanying person capable of providing the necessary assistance shall be transported free of charge and, where feasible, seated next to the person with disability
3. The accompanying person pays the standard fare but is guaranteed an adjacent seat
4. The accompanying person must travel in a separate following vehicle