Answer:
C). The reader could learn how to avoid getting the flu.
Step-by-step explanation:
In the given excerpt from 'Heart about the Flu', if the author cite or provide information about the sources that he has referred to, it would 'assist the readers to learn about the preventive measure to avoid the flu.' Since the author makes a number of deductions like 'people need to be...every year', 'vaccines must be produced..actual flu virus',etc., the citation of the sources would not only help the reader to refer to it for seeking information regarding the measures to prevent flu but also establish the credibility of his claims. Thus, option C is the correct answer.