The Following Questions Refer to the Excerpt Below

The following questions refer to the excerpt below.
"…You should support him,not because he is a negro gentleman,but because his record is consistent.For years he has been the only Republican Senator from the Southern section where the party has lost control,and hundreds of thousands of citizens are on the verge of disfranchisement who occupies his place without question,and that his official conduct is without reproach,and approved by all parties,while his political vote has been invariably cast with the Republican party is a fact….The nomination of Mr Bruce would culminate the idea of Horace Greely,of Thaddeus Stevens,of Abraham Lincoln,of Chas Sumner,of Ulysses Grant,of Jas G.Blaine,of Jno Sherman,and indeed of the great Republican party and relieve the nation at once of the question of caste in American politics.Horace Greely said of the finance the way to "resume is to resume" and the party should understand that the way to execute the constitution and the laws is to show determination to execute them."
Circular Letter by J.Milton Turner to Republican delegates at the National Convention to nominate a Presidential candidate,May 20,1880
-Which of the following historical events most directly made possible the circumstances in this excerpt?

A) The Emancipation Proclamation
B) The 13^th, 14^th, and 15^th amendments
C) The Force Acts
D) The Civil Rights Act of 1866