The most accurate effect of Lincoln’s issuing of the Emancipation Proclamation among the options provided is: It won the sympathy of Europeans, making it less likely for them to support the Confederacy. The Proclamation was a strategic move that reframed the Civil War as a fight against slavery, which resonated with many in Europe who were opposed to the institution of slavery, thereby reducing the likelihood of European nations supporting the Confederacy.
While it's true that abolitionists had mixed reactions and some felt the Proclamation did not go far enough, the other options regarding morale in the South and the status of slaves in the border states are not accurate in their implications. The Proclamation did not free slaves in border states, and while Southern morale was impacted, that effect is not as direct as the shift in international perception.