Explanation:

- The original sentence structure is "neither... nor," which requires the word "neither" to precede the verb for parallel construction. It should align as "is neither... nor."

- Option 1: "either is" doesn't work because "either... or" is not the intended phrase in this context.

- Option 2: "is neither" is the correct choice. It ensures the sentence follows the correct parallel structure.

- Option 3: "is either" is incorrect as it reverses the intended meaning and structure.

- Option 4: "is only" is irrelevant and changes the sentence meaning entirely.

- Option 5: "No correction required" isn't suitable as the original sentence's structure is off.