单选题 It is a multistep process, just as it is for seasonal influenza vaccine each year. However, the new H1NI virus did not emerge until April in this country, so the process started later than usual. In May, scientists produced a recombinant version of the virus that would grow well in eggs. Vaccine manufacturers take that new virus and inject it into millions of eggs, where the virus replicates. When enough virus has formed, manufacturers harvest the virus, inactivate it. extract individual proteins ~ from the viral coat, and combine those segments with other ingredients to produce a vaccine. The vaccine then has to pass tests for potency (效力) and sterility (纯净度). And clinical trials are needed to determine the optimal dose and number of shots that people will need. Trials for the H1N1 vaccine were announced in late July and should wind up around late September.
Clinical trials are needed for the purpose of

• A. determining the optimal dose and necessary shots.
• B. testing the potency and sterility of the vaccine.
• C. discovering the optimal way to make the injection.
• D. combining the vaccine with the proteins of the human body.