Solution:The pattern followed here is :In all the options, all letters are consecutive, except option c.
ABC → A + 1 = B, B + 1 = C
JKL → J + 1 = K, K + 1 = L
FGH → F + 1 = G, G + 1 = H
But,
RTU → R + 2 = T, T + 1 = U
Hence, RTU is the correct answer.