Why Were European Mobilization Plans So Inflexible

Why were European mobilization plans so inflexible?

A) They were extremely complex, involving millions of men, large amounts of matériel, and transportation infrastructure across very large distances.
B) European high commands had still not adopted virtually any modern military organizational principles, resulting in dramatic inefficiencies.
C) No European state had a standing army, so each had to recruit and train a large force in a very short amount of time to gain an advantage in any war.