The differences between the two is that autobiographies are when the author writes a biography about themself, versus biographies, where the author writes about another person. Biographies are not short stories, since they tend to write about a person's entire lifetime or a period of time. They aren't like science fiction since all biographies include true, proven facts. Poems are short pieces as well, and though there is a lot more detail to the definition of a poem, biographies have more in common with autobiographies than the other options.
