A: Who's riding the horse? B: a) It's brown. b) Fiona is!

Analysis:

This question asks for the identity of the person riding a horse. Option 'a' describes a characteristic (color), while option 'b' provides a name, which is a direct answer to 'Who'.

Answer (EN)

1. A: Who's riding the horse?
2. B: b) Fiona is!

Перевод (RU)

1. А: Кто едет на лошади?
2. Б: б) Фиона!