Final answer:
Medical emergency care riders are designed to cover sudden and severe conditions requiring immediate treatment. They provide essential assistance during emergencies and unforeseen medical needs.
Step-by-step explanation:
The type of rider that would cover immediate treatment sought and received for sudden, severe, and unexpected conditions is c. medical emergency care. This kind of rider typically ensures that individuals receive the necessary medical humanitarian assistance during urgent health incidents. Whether these incidents are due to accidents, natural disasters, clinical emergencies, or an unforeseen medical need, such riders aim to provide immediate response and coverage.