Check for each option whether all letters are present in the word REASONABLE.
- Option A: BRAIN
- Letters: B, R, A, I, N
- "I" is not in REASONABLE → Not Possible
- Option B: BONES → All letters are in REASONABLE
- Option C: NOBLE → All letters are in REASONABLE
- Option D: ARSON → All letters are in REASONABLE
\[
\boxed{\text{Only BRAIN cannot be formed}}
\]