What was Thomas Jefferson considered a 'contradiction'?

Arguably his most perplexing contradiction was that the man who wrote the inspiring words "all men are created equal" was a slave owner throughout his life. While contemporaries, including George Washington, freed their slaves, Jefferson kept his, even though he recognized the institution was wrong. Worse, this great scholar espoused abhorrently ignorant opinions about the physical and mental traits of blacks.

Source: https://www.sun-sentinel.com/news/fl-xpm-1997-02-18-9702140394-story.html

Ibelieve the answer is c

Not sure this is a hard one huh