Select the letter-cluster from among the given options that can replace the question mark (?) in the following series. XJ, AG, DD, GA, ?

KX JX KY JY

JX

Explanation: XJ, AG, DD, GA, ? The logic followed here is : X → (+3) → A → (+3) → D → (+3) → G → (+3) → J   J → (-3) → G → (-3) → D → (-3) → A → (-3) → X   So, the letter-cluster that replaces the (?) to complete the series is "JX"