Complete the letter pair sequence by identifying the next pair. Series: AI, BJ, CK, ?

Introduction / Context:
This is a classic letter-pair sequence question from verbal reasoning. Each pair follows a position-based pattern in the English alphabet. The task is to decode how the first and second letters of each pair progress and then extend the pattern to find the next pair.

Given Data / Assumptions:

• Given series of pairs: AI, BJ, CK, ?
• Alphabet positions used (A=1, B=2, …, Z=26).
• Exactly one pair continues the discovered pattern.

Concept / Approach:
Treat each component of the pair (the first letter and the second letter) as an independent sequence. Determine the step for the first letters and the step for the second letters, then apply those steps to produce the next pair.

Step-by-Step Solution:
First letters: A → B → C → ? (each step +1). So the next first letter is D. Second letters: I → J → K → ? (each step +1). So the next second letter is L. Combine results: the next pair is D + L = DL.

Verification / Alternative check:
Check consistency: (A,B,C,D) and (I,J,K,L) are both strictly consecutive runs. No irregularities appear, confirming DL fits uniquely.

Why Other Options Are Wrong:
.DM: Does not match the +1, +1 progression and contains an invalid leading character. GH: First letter would jump from C→G (+4) and second from K→H (−3), breaking the pattern. LM: First letter would be L instead of D, and second M instead of L; both violate the +1 steps.

Common Pitfalls:
Mixing up the two tracks (first vs. second letters) or looking for alternating or skipping patterns when a simple +1 progression explains the data.

Final Answer:
DL