Final answer:
The most appropriate sentence for academic writing is b. Psychologists who have clients with severe mental illnesses often tell them to establish a broad, supportive social network throughout their community.
Step-by-step explanation:
The most appropriate sentence for academic writing is b. Psychologists who have clients with severe mental illnesses often tell them to establish a broad, supportive social network throughout their community. This sentence demonstrates a formal and professional tone while effectively conveying the advice given by psychologists to clients with severe mental illnesses. It is clear, concise, and specific, making it suitable for academic writing.