Which of the following letter clusters will replace the question mark (?) and complete the following letter cluster series? OG, RL, XQ, GV, ?

SA RZ SB RA

SA

Explanation: OG, RL, XQ, GV, ? The logic followed here is : O → (+3) → R → (+6) → X → (+6) → G → (+9) → S G → (+5) → L → (+5) → Q → (+5) → V → (+5) → A   So, the letter-cluster that replaces the (?) to complete the series is "SA"