Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
ENU, FLS, GJQ, ?, IFM

ENU, FLS, GJQ, ?, IFM

Logic: 1st +1 , 2nd -2 , 3rd -2 

E +1 → F +1 → G +1 → H +1 → I

N -2 → L -2 → J -2 →H -2 → F

U -2 → S -2 → Q -2 → O -2 → M

So, missing letters = H H O

Thus, correct option is (a).