Which of the following letter-clusters will replace the question mark (?) and complete the following letter-cluster series?

DW, FU, GT, IR, JQ, ?

LO

Explanation:

DW, FU, GT, IR, JQ, ?

The logic followed here is :

D → (+2) → F → (+1) → G → (+2) → I → (+1) → J → (+2) → L

W → (-2) → U → (-1) → T → (-2) → R → (-1) → Q → (-2) → O

So, the letter-cluster that replaces the (?) to complete the series is "LO"