Select the letter cluster from among the given options that can replace the question mark (?) in the following series.
HIF, KLI, NOL, QRO, (?)

Given: HIF, KLI, NOL, QRO, (?)

Logic: In the given alphabetical series, add 3 to the place value of each letter of the given terms to get the next term.

First letter: H + 3 = K; K + 3 = N; N + 3  Q; Q + 3 = T

Second letter: I + 3 = L; L + 3 = O; O + 3 = R; R + 3 = U

Third letter: F + 3 = I; I + 3 = L; L + 3 = O; O + 3 = R

So, TUR is the missing term in the given series.

Thus, the correct answer is (a).