Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
GA, MU, SO, ?, EC
Answer & explanation
Correct answer: option 3

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"