Final answer:
The subject of this question is Health. The conclusion of the study is that all HMO patients should be urged to get a flu shot to prevent a serious case of the flu.
Step-by-step explanation:
The subject of this question is Health. The question is asking about the conclusion drawn from a follow-up study on randomly selected patients given a flu shot. The study found that none of the patients became seriously ill with the flu, leading to the conclusion that all HMO patients should be urged to get a flu shot to prevent a serious case of the flu.