In the sequence AB, DEF, HIJK, ?, STUVWX, which group of letters should replace the question mark to continue the pattern?

Introduction / Context:
This question involves a pattern of letter blocks in the English alphabet where both the starting letter and the length of each block change in a systematic way. It checks your ability to work with sequences of letters, not just single-letter jumps, which is a common theme in verbal reasoning tests.

Given Data / Assumptions:
- The given groups are: AB, DEF, HIJK, ?, STUVWX.- Each group consists of consecutive letters without gaps inside the group.- Both starting letters and group lengths appear to follow patterns.

Concept / Approach:
We should examine two things: the starting letter of each group and the number of letters in each group. Frequently, such series increase the group length step by step and shift the starting letter forward according to a separate rule. By understanding both patterns, we can accurately determine the missing group of letters.

Step-by-Step Solution:
- Count letters: AB has 2 letters, DEF has 3 letters, HIJK has 4 letters, and STUVWX has 6 letters.- The missing group should therefore have 5 letters to keep a gradual increase of 2, 3, 4, 5, 6 letters.- Look at starting letters: AB starts at A (1), DEF at D (4), HIJK at H (8).- Differences in starting positions: A to D is +3, D to H is +4, so the next difference should be +5.- H is position 8, so the next start is 8 + 5 = 13, which is M.- A 5-letter block from M is: M, N, O, P, Q giving MNOPQ.- Finally, 6-letter block from S gives STUVWX as in the question, so the pattern is consistent.

Verification / Alternative check:
- Confirm lengths: 2, 3, 4, 5, 6 form a clear increasing sequence.- Confirm starts: A (1), D (4), H (8), M (13), S (19) have increments of +3, +4, +5, +6.- These two coordinated patterns clearly identify MNOPQ as the only valid missing group.

Why Other Options Are Wrong:
- QRSTU starts at Q, not at M, and does not maintain the correct increment for the starting letters.- LMNO has only 4 letters, so it violates the required group length of 5.- LMNOP starts at L instead of M, so it breaks the start-position pattern, even though it has 5 letters.- Only MNOPQ satisfies both the starting position and group length patterns simultaneously.

Common Pitfalls:
Students often focus only on the number of letters and ignore the starting letter pattern, or vice versa. Another mistake is to pick the group that looks alphabetically closest without verifying both conditions. Always check both the starting position and the length of each block when dealing with such letter-series questions.

Final Answer:
The missing group of letters is MNOPQ, so the correct option is MNOPQ.