Ques. about the Fall of the Roman Empire

[LibDemAlways]

My 8th grader has a standardized history test coming up in a few weeks and was given a review study guide covering the main topics from 6th and 7th grades in the form of Multiple Choice Questions.

This one has her stumped. She's been looking up info on the internet and believes that all four answers are correct and can be supported. Is this your reading as well or is she missing something?
Any help would be appreciated, as I'd like for her to have accurate info to study from.

All were causes of the fall of the Roman Empire EXCEPT
a. slavery
b. inflation
c. size of the empire
d. lack of an army

[Odin2005]

1. The answer is (a) or (d). The size of the army actually grew during the late empire.

IMO slavery didn't have much to do with the cause of the collapse of the empire. What it DID cause was the fall of the republic as a result of aristocrats driving farmers off thier land and turning the land into slave-worked agribusinesses (Latifundia). The dispossessed farmers became the urban mob that became tools of demagogues like Gaius Marius and Julius Caesar.