Sentence Correction

source: jamboree blue book drill-1 sc
my pick (c)
seriously doubt the "reason that" usage here....sounds to me as if reason was engaged in espionage by us citz.


High-ranking security officials agree that ideology is no longer the main reason that United States citizens engage in espionage, as it was in the 1940's and 1950's; the chief motive now is money.

(A) that United States citizens engage in espionage, as it was
(B) for United States citizens engaging in espionage, as
(C) for United States citizens who engage in espionage as was so
(D) of United States citizens who engage in espionage, as it was
(E) United States citizens engage in espionage, as

oaa

This is an 'idiom' question

The correct idioms for "reason" include
(a) the reason to do X
(b) the reason for Q
(c) the reason for P to do X
(d) the reason that P does X

(A) is the only one that gets the idiom for "reason" correct.