d fits because proving one direction of a relationship (not enough pay = switch jobs) doesn't mean the other direction is necessarily true (enough pay = un-switch jobs), like proving p -> q doesn't prove !p -> !q, maybe the capable administrators made a bunch of new friends at their private sector jobs and don't want to change back, the passage just says raising salaries -> recapture administrators -> functioning improves without any new explanation, and it's necessary for the argument, so d is correct

for b, "presupposes" feels more like a "the argument needs this but doesn't establish it" sorta thing, so the last sentence explicitly saying recapturing administrators = improves functioning doesn't fit and it's kinda supported by other bits in the passage

also the conclusion is only that it improves functioning, so b goes too far, lots of stuff could improve functioning or be bigger factors and the argument could still be true

interested

Interested

Interested