A two letter series is given as CD, HI, NO, UV, ? Based on positions in the English alphabet, which pair of letters should come next to continue the pattern?

Introduction / Context:
This alphabet test question presents a series of two letter pairs: CD, HI, NO, UV, followed by a missing pair. The pattern involves both the progression of starting letters and the structure of each pair as adjacent letters in the alphabet. Once we convert to numeric positions, a simple pattern of increasing gaps becomes visible, which we can extend to find the next pair.

Given Data / Assumptions:

• Series: CD, HI, NO, UV, ? • Options: LM, NP, CD, NP (the last two are duplicates in the original options but we consider them as distractors). • Alphabet positions: C 3, D 4, H 8, I 9, N 14, O 15, U 21, V 22. • Assumption: The pattern uses the starting letter of each pair and the fact that each pair consists of consecutive letters.

Concept / Approach:
Each term is a pair of consecutive letters in the alphabet (like C and D, H and I, and so on). The key is to look at the starting letters C, H, N, and U and analyse how they progress numerically. Then we apply the same rule to obtain the next starting letter and form the pair by taking the next alphabet letter immediately after it. This two stage reasoning ensures that both structure and position are preserved.

Step-by-Step Solution:
Step 1: Confirm that each pair uses consecutive letters: C and D (3 and 4), H and I (8 and 9), N and O (14 and 15), U and V (21 and 22). Step 2: Consider the starting letters C, H, N, and U. Their positions are 3, 8, 14, and 21. Step 3: Find the differences between these positions: 8 − 3 = 5, 14 − 8 = 6, 21 − 14 = 7. Step 4: The differences are increasing by 1: 5, 6, 7. Therefore the next difference should be 8. Step 5: Apply this to the last starting position: 21 + 8 = 29. Since there are 26 letters, subtract 26 to wrap around the alphabet: 29 − 26 = 3, which is position of C. Step 6: So the next starting letter cycles back to C. Step 7: Each pair uses consecutive letters, so after C comes D. Hence the next pair is CD.

Verification / Alternative check:
We can view the starting positions as 3, 8, 14, 21, and then 3 again after wrapping, reflecting a pattern where each gap increases by one. The series is therefore cyclic and returns to CD after UV. Among the options, only CD preserves both the starting letter pattern and the consecutive letter structure inside the pair. LM and NP do not emerge from the described increasing difference pattern and so do not fit the series logic.

Why Other Options Are Wrong:
LM has starting letter L at position 12, which cannot be obtained by adding 8 to 21 and wrapping modulo 26. NP also fails the calculated starting position rule and would break the observed pattern of increasing gaps among starting letters.

Common Pitfalls:
A common mistake is to focus only on the fact that each pair uses consecutive letters and then pick any other consecutive pair like LM or NP. Without examining how the starting letters progress numerically, this leads to wrong answers. Always look at both the internal structure of each pair and the progression of their starting letters across the series.

Final Answer:
The pair of letters that continues the series CD, HI, NO, UV is CD (the pattern cycles back to the beginning).