Select the option that best completes the letter analogy: PEN : NEP :: CUP : ?

The group is simply written backwards: PEN read from the right is NEP. Reading CUP from the right gives P, U, C, that is PUC. Each distractor shuffles the same three letters into a different order — 'CPU' is a familiar-looking cluster that catches the eye, but only PUC is the true reversal.