Q: This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.
Passage: Popper left school at the age of 16 and attended lectures in mathematics, physics, philosophy, psychology and the history of music as a guest student at the University of Vienna. In 1919, Popper became attracted by Marxism and subsequently joined the Association of Socialist School Students. He also became a member of the Social Democratic Workers' Party of Austria, which was at that time a party that fully adopted the Marxist ideology. After the street battle in the Horlgasse on 15 June 1919, when police shot eight of his unarmed party comrades, he became disillusioned by what he saw to be the "pseudo-scientific" historical materialism of Marx, abandoned the ideology, and remained a supporter of social liberalism throughout his life. Question: Which Austrian political party did Popper join as a youth?
A:
Social Democratic Workers' Party of Austria