Critical Reasoning

Source: Peterson master GMAT 2010 (test 2).

More airplane accidents are caused by pilot error than any other single factor.
The military recently stopped requiring its pilots to obtain immunization shots
against chemical warfare agents. These shots are known to cause unpredictable
dizzy spells, which can result in pilot error. Since many military pilots also
pilot commercial passenger airlines, the reason for the military's decision must
have been to reduce the number of commercial airline accidents.
Which of the following, if true, provides most support for the conclusion drawn
above?

a) Recently, more pilots have been volunteering for the immunization shots.
b) All commercial airline flights are piloted by two co-pilots, whereas military flights are usually piloted by only one.
c) Chemical warfare is likely to escalte in the future
d) Military pilots are choosing to resign rather than obtain the immunization shots.
e) Recently, the number of military pilots also piloting commercial airlines has declined.

[spoiler]OA c IMO d, if somebody could explain why c is correct? [/spoiler]