Maybe someone could help me out with this. Why is the official answer the best answer?
10. Although Napoleon’s army entered Russia with far more supplies than they had in their previous campaigns, it had provisions for only twenty-four days.
(A) they had in their previous campaigns
(B) their previous campaigns had had
(C) they had for any previous campaign
(D) in their previous campaigns
(E) for any previous campaign
Very simple ... Napoleon's Army is a collective noun so considered a singular.
A, B, C, D all start with a plural.
Also E is parallel i.e for any previous campaign , ... for only twenty-four days.
So E is the best ans.
The only way of finding the limits of the possible is by going beyond them into the impossible.