What advantage did the allies have at the outbreak of world war 1.
a. better industrial resources
b. a military plan of action
c. the ability for better and faster communication
d. the ability to move men and supplies more freely

The Allied forces at the outbreak of World War I had better industrial resources and a military plan of action. I would say that both answers (A and B) could be considered correct here because for the Antante forces only Germany was a heavily industrialized nation, for the Allied forces, however, France and Great Britain alone were massively industrialized and had an enormous production. Moreover, while the Antante forces had an military plan of action, so did the allies and theirs proved to be better after all. 

It is c because it shows how the author is stating their own oppinion about the protagonist