Answer:
B.
Step-by-step explanation:
A. is incorrect as: "such persons of suitable conditions will be received into the armed service of the United States," essentially saying that blacks will be accepted into the army.
B and D are not related to the passage at all, really.
So why would B be correct?
Slaves have military importance because they could be placed in critical positions such as "garrison forts, positions, stations, etc."
Lincoln says that freeing the slaves will be "an act of justice" out of "military necessity."