The correct answer is **You ought to follow the doctor's instructions carefully.** (Option 1). **Comprehensive Derivation:** The correct answer is "You ought to follow the doctor's instructions carefully." Explanation & Key Takeaways: • In the active voice, the sentence structure is: • [Subject] + [Verb] + [Object] • The subject in the passive sentence is 'The doctor's instructions.' In the active voice conversion, 'The doctor's instructions' becomes the object. • The verb in the passive voice sentence is 'be followed', which is the past participle form of 'follow'. • In transforming the sentence into active voice, we should use 'follow' as the verb. • The words 'ought to' indicate necessity or duty, and they remain in the active voice version. Therefore, the correct answer is "option 1". **Option Elimination:** • **Option 1 (You ought to follow the doctor's instructions carefully.)**: Correct Answer; accurate according to canonical reference. • **Option 2 (It is ought to follow the doctor's instructions carefully.)**: Incorrect distractor. • **Option 3 (Ought they follow the doctor's instructions carefully?)**: Incorrect distractor. • **Option 4 (Carefully doctor's instruction ought to be followed.)**: Incorrect distractor. **Exam Trap:** Be careful of misleading distractors and subtle terminology differences. Verify core properties before selecting your answer. **Memory Booster:** Core mnemonic rule: You ought to follow the doctor's instructions carefully. corresponds to Option (1).