In the following series of letter pairs, one pair is missing. Choose the correct pair that continues the pattern: MN, PQ, TU, YZ, ?

Introduction / Context:
This alphabet series question involves pairs of consecutive letters. The series moves forward through the alphabet with changing step sizes. You must determine the size of each jump and then use it to find the next pair. Identifying variable increments is an important pattern recognition skill.

Given Data / Assumptions:

• Given pairs: MN, PQ, TU, YZ, ? • Each pair contains two consecutive letters (M with N, P with Q, and so on). • Moves between pairs may wrap around the alphabet beyond Z. • The same rule is applied to both letters of each pair.

Concept / Approach:
To solve this kind of problem, look at the first letters only: M, P, T, Y. Convert them into numbers and check the differences. If the increment changes regularly, you can extrapolate the next step. Since each pair contains consecutive letters, once you know the starting letter, the second letter is determined automatically as the next one in the alphabet.

Step-by-Step Solution:
Step 1: Convert the first letters to positions. M = 13, P = 16, T = 20, Y = 25. Differences: 13 → 16 is +3, 16 → 20 is +4, 20 → 25 is +5. The increment itself increases by 1 each time. Step 2: Continue the pattern for the next first letter. The next jump should be +6: 25 + 6 = 31. Since the alphabet has 26 letters, 31 − 26 = 5, which corresponds to E. Step 3: Determine the second letter of the pair. Each pair contains consecutive letters, so the second letter is the next after E, which is F. Thus, the missing pair is EF.

Verification / Alternative check:
Check the full numeric sequence of first letters: 13, 16, 20, 25, 5. The differences are +3, +4, +5, +6 (with wrap around). If we build pairs from these starting letters, we get MN, PQ, TU, YZ, and finally EF. This respects the pattern perfectly. None of the other options produces a starting letter that matches the expected numeric result after wrapping.

Why Other Options Are Wrong:
• YZ: Repeating the last given pair fails to continue the increasing step pattern. • AB: A would correspond to position 1, and the step from 25 to 1 is −24 or +2, which does not match the expected +6 step. • EJ: While E appears, J is not the consecutive letter after E and therefore breaks the structure of consecutive letter pairs.

Common Pitfalls:
One pitfall is to assume that the sequence restarts at A after Y without checking the exact step size. Another is to focus only on visual closeness, such as AB appearing near the start of the alphabet, instead of actually computing numeric distances. Always confirm the increment pattern before choosing an answer.

Final Answer:
The letter pair that correctly completes the series is EF.