The symptoms of hepatitis A appear no earlier than 60 days after a person has been infected. In a test of a hepatitis A vaccine, 50 people received the vaccine and 50 people received a harmless placebo. Although some people from each group eventually exhibited symptoms of hepatitis A, the vaccine as used in the test is completely effective in preventing infection with the hepatitis A virus. Which one of the following, if true, most helps resolve the apparent discrepancy in the information above? ['The people who received the placebo were in better overall physical condition than were the people who received the vaccine.', 'Of the people who developed symptoms of hepatitis A, those who received the vaccine recovered more quickly, on average, than those who did not.', 'The vaccinated people who exhibited symptoms of hepatitis A were infected with the hepatitis A virus before being vaccinated.', 'The placebo did not produce any side effects that resembled any of the symptoms of hepatitis A.']