The correct letter is A.
Just over two months after President Lincoln ( member of the Abolitionist Republic Party) was elected, he saw the first state to succeed when South Carolina voted to secede on December 20th 1860
South Carolina seceded from the Union of the United States due to increasing fears that northern, non-slavery states would impede the rights of southern states to keep slaves.
In the 1860 election was seen as the last straw from most slave-holding states in the South. In December of 1860, after Lincoln was elected, the government of South Carolina drafted a formal ordinance declaring their secession from the United States.
On April 12, 1861, South Carolinian forces opened fire on U.S. Army troops held up at Fort Sumter, an act which is generally regarded as the official beginning of the Civil War.