Final answer:
The important legislation passed by Abraham Lincoln was the Emancipation Proclamation, which declared the freedom of slaves in Confederate territory and was a critical step towards ending slavery in the United States.
Step-by-step explanation:
One important legislation passed by Abraham Lincoln was a) The Emancipation Proclamation. This pivotal document was issued by Lincoln in 1863, during the American Civil War, declaring all slaves in Confederate-held territory to be forever free. The proclamation paved the way for the abolition of slavery in the United States. Although the document did not immediately free all enslaved people, as it only applied to territories not under Union control, it was a critical step towards emancipation and symbolized a definitive Union policy to end slavery.
The other options listed, including The Social Security Act, The Voting Rights Act, and The New Deal, are associated with legislation passed during the presidency of Franklin D. Roosevelt in the 1930s and 1960s, and they were not enacted by Abraham Lincoln.