Choose the odd one out.

The odd one out is D. RXTO.

All the other options have the same pattern: the first and third letters are the same, and the second and fourth letters are the same. For example, in A. DJFB, the first and third letters are D and F, and the second and fourth letters are J and B.

In D. RXTO, the first and third letters are R and X, but the second and