Final answer:
The author's choice of narrator is third-person narration.
Step-by-step explanation:
This is what is known as third-person narration. The voice does not belong to a particular character in the novel, and in the extract it does not assume the perspective of any of the characters, merely describing their physical appearance, social status and relationships, and, in Catherine's case, her likes and dislikes, her accomplishments and pastimes. You will probably have noticed that this extract comprises a single, extremely long paragraph and is mostly concerned with describing the young Catherine Morland. This amount of detail at the start of the novel suggests to us that Catherine is likely to be the central character, and so it proves.