Given the task definition and input, reply with output. In this task, you're given an article, a question which often contains a blank and four options (associated with "A", "B", "C", "D"). Your task is to find the correct answer (from the given options) for the question from the given article and return one of the options from "A", "B", "C", and "D". Do not generate anything else apart from one of the following characters: "A", "B", "C", "D". There is only one correct answer for each question.

Article: President Abraham Lincoln's first call for volunteers to fight in the Civil War was for whites only.The Civil War was a white man's war,northern whites insisted.Its purpose was to preserve the Union.It was not being fought to end slavery.But by September of 1862,the _ toward black volunteers had changed.Lincoln had hoped that the war would be short,but it had already lasted for a year and a half.Union manpower had fallen dangerously. Lincoln had a plan.He issued the Emancipation Proclamation.It stated that as of January 1,1863,all slaves living in the rebellious southern states would be forever free.And starting immediately,Union armies would accept black volunteers. The southern rebels'response to Lincoln's call for black troops was a deadly one.Captives of any Union regiment with black troops were to be given "no quarter".They were to be put to death immediately. AfricanAmerican troops throughout the war distinguished themselves in battle at places like Milliken's Bend,Fort Wagner,and the Crater at St.Petersburg.As to their conduct on the battlefield,Colonel Thomas Wentworth Higginson wrote,"Nobody knows anything about these men who has not seen them in battle.No officer in this regiment now doubts that the successful process of the war lies in the unlimited employment of black troops." By the war's end,186,000 black men had participated.They made up nearly 10 percent of Union forces.These black soldiers saw action in more than 250 battles.Black soldiers also gave their lives.By the war's end,about 38,000 black soldiers had died.They died from disease,in battle,and after capture by rebel troops.
Question: This passage is mainly about _ .
Options: (A) cause of the Civil War (B) the Emancipation Proclamation (C) black soldiers in the Civil War (D) why Lincoln was a good president
C