The rule can also be pictured as pairing up the alphabet from 'e' onward into two-letter blocks, (e,f), (g,h), (i,j), (k,l), (m,n), (o,p), (q,r), (s,t), (u,v), (w,x), (y,z), where only the first letter of each pair is capitalised and the second stays lower-case; a, b, c, d, before 'e', are never capitalised. The sixth month from March is September, so 'september' is checked pair by pair: s falls in the pair (s,t), taking the capital first slot, while t takes the lower-case second slot; e falls in the pair (e,f), taking the capital first slot; m falls in the pair (m,n), taking the capital first slot; b falls before the paired region entirely, so it stays lower-case; the repeated e is again the first of its own pair, so it is capital; r falls in the pair (q,r), taking the lower-case second slot.
Only option B places every letter of 'september' on the correct side of its pairing.
Therefore, the correct answer is SEptEMbEr.