AEFG, BHIJ, ?, DNOP

Answer: CKLM is correct.

Key idea: the sequence hides two interleaved patterns.

• First-letter series: A, B, C, D (these advance one letter at a time).

• Three-letter blocks: EFG, HIJ, KLM, NOP (each block is three consecutive letters).

Mapping these together gives A → EFG, B → HIJ, C → KLM, D → NOP. Therefore the missing entry paired with C must be KLM, producing CKLM.