​Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
HFD KIG NLJ QOM ?

​HFD KIG NLJ QOM ?

1st letters: H → +3 → K → +3 → N → +3 → Q → +3 → T
2nd letters: F → +3 → I → +3 → L → +3 → O → +3 → R
3rd letters: D → +3 → G → +3 → J → +3 → M → +3 → P

So, the next term is: TRP.

Thus the correct option is: (a)