The answer is :

Explanation---there are a gap of 1 letter in between each letter in each group and a difference of two letters in between each group. So, after BDF, we will ignore two letters after F i.e. G and H and continue with I. Then, we will leave a letter after I i.e. J and continue with K. Likewise, we get IKM to be the answer.

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Since in the sequence there is a gap of two letters between the last letter of previous sequence and comin sequence and 1 letter gap within a sequence, so keeping this in mind the answer is IKM [ I comes after leaving two letters from F, K comes after leaving one letter from I and M comes after leaving one letter from K..... So the answer is ----> IKM...
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