Three of the following four letter-clusters are alike in a certain way and one is different. Pick the odd one out.

Option A - Alphabetical difference in EGK, between E and G is 2 and between G and K is 3.

Option B - Alphabetical difference in IKM, between I and K and K and M is 3. 

Option C - Alphabetical difference in BDH, between B and D is 2 and D and H is 4.

Option D - Alphabetical difference in DFJ, between D and F is 2 and F and J is 4.

hence only option B having the same difference between the alphabets among other options.