In the alphabet series A, D, H, M, which letter should appear next to extend the pattern correctly?

Introduction / Context:
This question involves a series of single letters: A, D, H, M. The objective is to find the next letter in sequence by analysing the changes between consecutive terms. Even though only four letters are shown, they hide a simple pattern in the numerical positions of the letters. Identifying such patterns is a core skill in alphabet-test and series-based aptitude questions.

Given Data / Assumptions:

• Given series: A, D, H, M, ?.• Each term is a single capital letter.• The alphabet positions are A=1, B=2, ..., Z=26.• We assume a regular growth pattern in the differences between consecutive letters.

Concept / Approach:
We first convert each letter into a number according to its position in the alphabet. Then we calculate the differences between these numbers. If the differences themselves form a simple sequence (for example, increasing by 1 each time), we can apply this to compute the next term. This is a common structure in single-letter alphabet series, where the series of differences is often more informative than the letters alone.

Step-by-Step Solution:
Positions: A=1, D=4, H=8, M=13.Differences: 4 − 1 = 3, 8 − 4 = 4, 13 − 8 = 5.Thus, the increments are +3, +4, +5, increasing by 1 each time.The next increment should logically be +6.Next letter position = 13 + 6 = 19, which corresponds to S.

Verification / Alternative check:
Writing the full numeric series including the next term gives 1, 4, 8, 13, 19. The second differences are 1, 1, 1, confirming that the first differences grow by 1 at each step. This matches a simple quadratic-type growth in numeric terms but is easy to handle in the alphabet context. Substituting 19 back to S verifies that the choice S maintains the consistent pattern.

Why Other Options Are Wrong:
R corresponds to position 18, which would give an increment of +5 from M, repeating the previous increase instead of continuing the pattern. Q and T correspond to 17 and 20 respectively, giving increments of +4 and +7, which are inconsistent with the established +3, +4, +5, +6 progression. Hence, none of these alternatives respect the precise incremental growth found in the given series.

Common Pitfalls:
Some candidates stop after noticing that the letters seem to be spaced by roughly three or four positions and guess randomly among nearby letters. Others do not compute the sequence of differences carefully and miss the fact that the difference itself is increasing steadily. A disciplined calculation of letter positions and their differences prevents such errors.

Final Answer:
S