If the narrator of a fictional piece is not a character in the story, which statement about the narrator is tru
the narrator of the work is always known as the speaker
the narrator is the historical author of the piece
the narrator speaks using an authonial voice
the narrator will speak from a third person point of view

I feel like more context is needed in order to properly address this question.

Explanation:

If the narrator is the sole speaker of the piece— that is to say, the characters themselves are referred to in 3rd person— the narrator is likely always known as the speaker.

If the narrator speaks with the author's voice— so the author explicitly inserts himself/herself, by name, in the piece— then the narrator is the historical author.

Authorial voice kind of sounds the same as the previous statement...

The narrator speaks in a third person point of view when he/she refers to the characters by name— so in third person. Whether the narrator is, or not, omniscient would depend on whether he/she is privy to the characters' inner thoughts

- the heat nearly killed them that first summer.