Answer: C. "I do not know which of us has written this page."
Explanation: In "Borges and I" by Jorge Luis Borges, the piece of textual evidence that best supports the main character's dual existence is the above mentioned. The unnamed narrator tells us about Borges. Borges is the one who has written some decent pages. The narrator is someone different from Borges. The narrator is the real person under the public character of Borges. The private self that explores the relationship with Borges. Borges is the public persona, the one known by others. In the end, the narrator claims he does not know which of the two has written these lines.