The verified answer to “In a certain code, CAT is written as DBU. How will PENS be written in that code?” is QFOT, option D. The source working states: Correct answer: QFOT (Option A). Apply the same unchanged rule to PENS: P→Q, E→F, N→O, S→T. Therefore the required code is QFOT. Wrong options: RGPU is wrong because it does not reproduce the verified rule at every position; ODMR is wrong because it does not reproduce the verified rule at every position; NCLQ 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 QFOT. The alternatives RGPU, ODMR and NCLQ fail because at least one position does not obey the same transformation. A useful final check is to map QFOT backward through the inverse operation and confirm that the original target is recovered.