Until now, only injectable vaccines against influenza have been available. They have been used primarily by older adults, who are at risk for complications from influenza. A new vaccine administered in a nasal spray has proven effective in preventing influenza in children. Since children are significantly more likely than adults to contract and spread influenza, making the new vaccine widely available for children will greatly reduce the spread of influenza across the population. Which of the following, if true, most strengthens the argument? ['The new vaccine uses the same mechanism to ward off influenza as injectable vaccines do.', 'Of the older adults who contract influenza, relatively few contract it from children with influenza.', 'Many parents would be more inclined to have their children vaccinated against influenza if the vaccination did not require an injection.', 'Government subsidies have kept the injectable vaccine affordable for all older adults.']