Final answer:
The best scenario that illustrates adverse selection is option b, where individuals who have existing medical conditions but are not physically apparent, decide to take up health insurance.
Step-by-step explanation:
The best scenario that illustrates adverse selection is option b, where individuals who have existing medical conditions but are not physically apparent, decide to take up health insurance. Adverse selection occurs when riskier individuals buy insurance while less risky individuals do not. If only sick(er) people buy insurance, the cost of insurance becomes extremely expensive. This is a common problem in insurance markets, where buyers have more information about their risk levels than the insurance company.