Which of the following letter-clusters will replace the question mark (?) in the given series? RI, PK, LO, FU, XC, ?
- A.PK
- B.MN
- C.NM
- D.NL
Explanation
1st letter diffs −2,−4,−6,−8,−10 (R,P,L,F,X,N). 2nd letter diffs +2,+4,+6,+8,+10 (I,K,O,U,C,M). Missing = NM.