Two of the more memorable characters whom Alice encounters during her journey through the Looking-Glass land are Tweedledee and Tweedledum.
Explanation:
The best revised sentence contains the same information as the original one, but in more formal, richer language: that Alice comes across Tweedledee and Tweedledum, who are very peculiar characters.
The rest of the choices are incorrect because they do not reflect with accuracy the meaning of the informal sentence, and not all of them are written in a formal register for an essay.
"<span>Two of the more memorable characters whom Alice encounters during her journey through the Looking-Glass land are Tweedledee and Tweedledum." Would be correct.</span>
