From the given options, select the term which can replace the question mark (?) in the following sequence.
SR1, PO3, LK9, ?

SR1, PO3, LK9, ?

Logic: First letters decrease by -3, -4, -5; second letters decrease by -3, -4, -5; numbers multiply by 3 each time.

S - 3 = P, P - 4 = L, L - 5 = G
For R → O → K → ?

R - 3 = O, O - 4 = K, K - 5 = F

1 × 3 = 3, 3 × 3 = 9, 9 × 3 = 27

So, GF27 is next term.

Thus, the correct answer is (a).