Fill up the blank with the correct word: My father keeps all his __________ papers under lock & key.

Correct answer: confidential

Explanation: Context: The word ‘confidential’ means secret or private. It refers to important information meant to be kept safe or undisclosed. 1. confidential ✅ – correct; means private or secret. 2. necessary ❌ – means essential, not secret. 3. required ❌ – means needed. 4. useful ❌ – means helpful, not private. Correct Sentence/Example Sentence: My father keeps all his confidential papers under lock and key.