A. After Robert E. Lee surrendered
The 16th President of the United States, Abraham Lincoln, was inaugurated to his second term on March 4, 1865, and a month later he was assassinated, on April 15th, 1865 (This fact proves D is incorrect).
Six days before the President was killed, on April 9, 1865, General Robert E. Lee of the Confederate Army had surrendered to Lieutenant General Ulysses S. Grant, the Union Army leader (OPTION A: CORRECT). This date is also referred as the end of the American Civil War (Therefore, option B is incorrect too).
Option C is also incorrect because the American Civil War started on April 12nd, 1861.
