Scientists recently documented that influenza spreads around the world more efficiently in the modern era due to commercial air travel. Symptoms of a pandemic-level flu are severe enough that the ill would likely cancel or reschedule air travel, but an infected person can travel across the globe before the first signs appear. Further, if symptoms develop while someone is still on a plane, the infected person's cough can spread the virus easily in the enclosed and closely packed environment.
Which of the following would best minimize the role air travel can play in the spread of influenza during a pandemic?

(A) installing air filtration systems in the planes to kill any flu virus particles flowing through the filters
(B) requiring air travelers to receive flu vaccinations far enough in advance of the trip to provide protection against the disease
(C) refusing to allow children, the elderly, or others who are especially vulnerable to flu to travel by air during a pandemic
(D) requiring all air travelers to wash their hands before boarding a plane
(E) conducting medical examinations during the boarding process to weed out passengers with flu symptoms

[spoiler]Answer per Manhattan B. IMO E.
Reason for rejecting B: even if travelers receive flu vaccinations, they may be infected on the date of travel (as we are not told how many vaccinations they will take so as not to be infected, which if we assume, I feel we are bringing outside knowledge something which a test taker needs to avoid.

Also, B has a catch: person with symptoms will LIKELY (not certainly) cancel/reschedule the travel. So, it cannot be said with certainty whether infected person/person with flu symptoms will not travel, and hence less impact of air travel.

Reason for selecting D: such examination will ensure only the persons who are neither infected nor have any flu symptoms (albeit early stage symptoms).[/spoiler]