The correct answer is A, as the statement is true. General George McClellan was Lincoln's Democratic opponent in the 1864 election.
In the Presidential Election of 1864, Abraham Lincoln was reelected as president. Lincoln competed under the flag of the National Union against his former superior general in the Civil War, the Democratic candidate, George B. McClellan. McClellan was the "candidate for peace", but he did not personally share the ideologies of his party.
On November 8, Lincoln won by more than 400,000 popular votes and easily secured an electoral majority.