Select the letter-pair that can replace the question mark (?) in the following series. AR, CU, EX, GA, ?

JE ID IF KF

ID

Explanation: AR, CU, EX, GA, ? The logic followed here is : A → (+2) → C → (+2) → E → (+2) → G → (+2) → I   R → (+3) → U → (+3) → X → (+3) → A → (+3) → D   So, the letter-cluster that replaces the (?) to complete the series is "ID"