The correct option is D MP
Here, in each of the pair, the second letter is three steps ahead of the first letter. Now, the next pair has the first letter which is immediate after the previous letter in previous pair and again the second letter of the next group is three steps ahead of the previous letter in the alphabetic series and this pattern continues.
Clearly, the next letter after L is M. Now, the letter which is 3 steps ahead of M is P.
So, MP is the pair which will fill the blank.
Hence, option (D) is the correct answer.