Which of the following letter-clusters will replace the question mark (?) and complete the following letter-cluster series ? LE, OJ, UO, DT, ?

PZ QY PX PY

PY

Explanation: LE, OJ, UO, DT, ? The logic followed here is : L→ (+3) → O → (+6) → U → (+9) → D → (+12) → P E → (+5) → J → (+5) → O → (+5) → T → (+5) → Y   So, the letter-cluster that replaces the (?) to complete the series is "PY"