Correct Answer: VTRP

Solution : Given:
LJHF : USQO :: QOMK : ?

The difference between the place value of the letters of the given letter cluster and its related letter cluster is constant –
L + 9 = U; J + 9 = S; H + 9 = Q; F + 9 = O

Let's check the options –
First option: QPSR; Q + 0 = Q; O + 1 = P; M + 6 = S; K + 7 = R (The difference between the place values of each letter is not constant.)
Second option: PNMK; Q – 1 = P; O – 1 = N; M + 0 = M; K + 0 = K (The difference between the place values of each letter is not constant.)
Third option: VTRP; Q + 5 = V; O + 5 = T; M + 5 = R; K + 5 = P (The difference between the place values of each letter is constant.)
Fourth option: YXWU; Q + 8 = Y; O + 9 = X; M + 10 = W; K + 10 = U (The difference between the place values of each letter is not constant.)

So, QOMK is related to VTRP. Hence, the third option is correct.