A is incorrect because Lincoln ran for the republican party.
D is incorrect because the Democratic party was pro-slavery.
So that leaves us with B and C.
I don't know who John C. Breckinridge is, but I do know that Lincoln was the least popular candidate running for president. The only reason Lincoln won the election was because the democratic party split their votes between two candidates, so neither democratic candidate got enough votes to win the election.
So the answer is B.