Select the letter-cluster from among the given options that can replace the question mark (?) in the following series. GA, MU, SO, ?, EC

ZI ZJ YI YJ

YI

Explanation: GA, MU, SO, ?, EC The logic followed here is : G→ (+6) → M → (+6) → S → (+6) → Y → (+6) → E A → (-6) → U → (-6) → O → (-6) → I → (-6) → C So, the letter-cluster that replaces the (?) to complete the series is "YI"