Final answer:
The correct word to complete the analogy is doctor. A car requires a mechanic to repair and maintain it, just like a body requires a doctor to diagnose and treat medical conditions.
Step-by-step explanation:
The correct word to complete the analogy is doctor. The relationship between car:mechanic is that a car requires a mechanic to repair and maintain it. Similarly, the relationship between body:doctor is that a body requires a doctor to diagnose and treat medical conditions.