The verified answer to “In a certain code, HEART is written as IDBQU. How will DOG be written in that code?” is ENH, option D. The source working states: Correct answer: ENH (Option A). Apply the same unchanged rule to DOG: D→E, O→N, G→H. Therefore the required code is ENH. Wrong options: EPH is wrong because it does not reproduce the verified rule at every position; FQI is wrong because it does not reproduce the verified rule at every position; CNF is wrong because it does not reproduce the verified rule at every position. Even one mismatched position invalidates a code, so only Option A is correct. This observation must be confirmed across every available letter position or every consecutive term before it is applied to the missing code. Applying the verified rule to the target expression produces ENH. The alternatives EPH, FQI and CNF fail because at least one position does not obey the same transformation. A useful final check is to map ENH backward through the inverse operation and confirm that the original target is recovered.