To solve the problem of identifying the missing letters in the series QPO, NML, KJI, _____, EDC, we need to identify the pattern in the sequence.
The series consists of groups of three consecutive reverse alphabet letters, and each subsequent group follows a decremental pattern. Let's break down the sequence:
- QPO: Here, Q (17th letter), P (16th letter), O (15th letter) are in descending order.
- NML: N (14th letter), M (13th letter), L (12th letter) are decrementing in the alphabet sequence.
- KJI: K (11th letter), J (10th letter), I (9th letter) continue in the descending order.
- ____: To find the missing letters, we continue the decremental sequence: H (8th letter), G (7th letter), F (6th letter).
- EDC: Lastly, E (5th letter), D (4th letter), C (3rd letter) follow the same decremental pattern.
Therefore, the missing set of letters that fits the sequence is HGF.
Upon reviewing the given options, the correct choice that completes the series is: HGF.