**Core Concept**: Vocabulary (synonym discrimination in context). **Analysis**: The sentence criticizes a doctor's improper medical practices. 'Aggressive' (C) implies excessive/unnecessary actions, fitting the negative tone. - **Correct Answer (C)**: 'Aggressive' implies forceful/overzealous actions, aligning with 'ineffective treatments'. - **Errors**: - A. 'Persistent' lacks contextual negativity. - B. 'Reluctant' contradicts the action described. - D. 'Cautious' opposes the implied criticism. **Key Point**: Contextual alignment of adjective connotations.