From the given alternatives, select the word which CANNOT be formed using the letters of the given word.
Unquestionable

Let's verify the letter availability from the word Unquestionable:
Able: A, b, l, e are all present. (Can be formed)

Untie: U, n, t, i, e are all present. (Can be formed)

Question: Q, u, e, s, t, i, o, n are all present. (Can be formed)

Nature: The letter 'r' is present in Nature, but 'r' is not present anywhere in the word Unquestionable.

Therefore, Nature cannot be formed.