In Terms of Manpower Needed to Fight the Civil War

In terms of manpower needed to fight the Civil War, the South was disadvantaged by

A) a smaller total population of military-aged males than the North.
B) limited support from free, white males in border states.
C) a population that included over 1 million military-aged slaves who could not be used for direct combat.
D) the fact that some of its manpower had to be used to repress the slave labor force.
E) All of the above.