Explanation:

- Let's break the pattern:

- YZ (2 letters)

- BCD (3 letters, starts after A)

- FGHI (4 letters, starts after E)

- ?

- QRSTUV (6 letters, starts after P)

- We observe: Number of letters increases by one each time. The first group has 2, then 3, then 4, then the missing group should have 5, and then 6 in QRSTUV.

- Check letter sequence:

- After YZ (Y is the 25th, Z is 26th), starts over at B (skips A possibly for pattern).

- After BCD, next is FGHI (after F, which comes after E).

- Gaps between groups: YZ to BCD skips A, BCD to FGHI skips E.

- For the fourth, after FGHI, the next group should be KLMNO (5 letters, starts after J).

- So, option 3: KLMNO is correct.

- Let's check all options:

- Option 1: JKLMN (5 letters, but starts at J, which disrupts pattern).

- Option 2: LMNOP (5 letters, starts too far, after L).

- Option 3: KLMNO (5 letters, fits perfectly in pattern)

- Option 4: JKLM (4 letters, only 4, should be 5)