Answer:
d. The extension of slavery to United States territories should be prohibited by the federal government, but slavery should be protected in the states where it already existed
Explanation:
Abraham Lincoln, the Republican candidate for the presidency in 1860, was morally opposed to slavery, but he also recognized that slavery was permitted by the existing law of the land, the US Constitution. So Lincoln's initial position on slavery -- and the platform of the Republican Party in 1860 -- was to stop the spread of slavery.
The Republican platform in 1860 rejected the idea that the Constitution allowed for the extension of slavery into any or all of the territories of the United States as "a dangerous political heresy." The party platform went on to say this: