Which of the following letter cluster will replace the question mark (?) to complete the given series?

SXP, PVO, MTN, ? , GPL

JRM

Explanation:

SXP, PVO, MTN, ? , GPL

The logic followed here is :

S → (-3) → P → (-3) → M → (-3) → J → (-3) → G 

X → (-2) → V → (-2) → T → (-2) → R → (-3) → P

P → (-1) → O → (-1) → N → (-1) → M → (-1) → L

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