Answer-Find the missing letters. CFI, EHK, (?), FKP, HMR, JOT.

There are two series CFI, EHK, GJM and FKP, HMR, JOT. The first letter in every group of the series comes after a gap of one letter, i.e., C, E, G, and the second and third letters of each group have the same sequence, i.e., FHJ and IKM. Same is the case with the second series.