Select the related group of letters from the given alternatives: DHL : PTX :: BFJ : ?

Introduction / Context:
This question belongs to the category of alphabetical analogies involving a fixed shift in letter positions. The pair DHL : PTX follows a specific coding rule. Your task is to detect this rule and then apply it to the group BFJ to determine which option is analogous to PTX. Such questions measure pattern recognition and familiarity with alphabetical position values.

Given Data / Assumptions:
- Alphabet positions are A = 1 through Z = 26.
- DHL and PTX each contain three letters, and there is a consistent transformation from each letter in DHL to the corresponding letter in PTX.
- The same transformation must be applied to all letters of BFJ to obtain the answer.
- Only one option will match the discovered pattern exactly.

Concept / Approach:
We convert letters to numeric positions, find the change applied to each letter in the first pair, and then use this change on the second word. Because DHL and PTX each have three letters, we check letter by letter to see whether a constant shift such as +2, +10, or +12 is present. If the shift is the same for all positions, we have a valid coding rule. Then we apply this same shift uniformly to BFJ.

Step-by-Step Solution:
Step 1: Convert the first word DHL to numbers. D = 4, H = 8, L = 12. Step 2: Convert the second word PTX to numbers. P = 16, T = 20, X = 24. Step 3: Find the difference for each position: 4 to 16 is +12, 8 to 20 is +12, and 12 to 24 is +12. Thus the rule is "add 12" to each letter position. Step 4: Write the positions of BFJ. B = 2, F = 6, J = 10. Step 5: Apply the same +12 shift. 2 + 12 = 14 (N), 6 + 12 = 18 (R), 10 + 12 = 22 (V). Step 6: Therefore BFJ becomes NRV when coded according to the same rule that maps DHL to PTX.

Verification / Alternative check:
To verify, you can reverse the transformation. Subtract 12 from N, R, and V. N (14) minus 12 gives B (2), R (18) minus 12 gives F (6), and V (22) minus 12 gives J (10). This confirms that the mapping is correct and symmetric. Additionally, none of the other answer options can be obtained by adding 12 to all three letters of BFJ, which strengthens the conclusion.

Why Other Options Are Wrong:
Option B "RVZ" would require different shifts for J, and the pattern would no longer be a constant +12 for all letters.
Option C "CGK" changes B to C by +1 and so does not match the +12 pattern at all.
Option D "KOS" uses mixed shifts and cannot be produced by one uniform rule, so it is inconsistent with the DHL to PTX transformation.

Common Pitfalls:
Students sometimes guess based on partial similarity, such as matching only the first letter. However, for a valid analogy, the coding rule must apply to every letter in the word. Another common error is treating positions modulo 26 without checking whether a simpler fixed shift explains the mapping. Always verify that the same numeric change works consistently across all positions.

Final Answer:
The correct related group of letters is NRV.