Which one of the following is not a part of early Jaina literature?

Therigatha is the correct answer because it is a Buddhist text, not a Jaina one. It is a collection of short poems authored by elder nuns and is part of the Khuddaka Nikaya of the Pali Canon. In contrast, the other three options are important early Jaina texts. Acarangasutra is the first of the twelve Angas and deals with the conduct of Jaina monks. Sutrakritanga is the second Anga, which focuses on Jaina philosophy and the refutation of other doctrines. Brihatkalpasutra is a text from the Chedasutras that contains rules and discipline for the monastic community. Therefore, Therigatha is the only one that belongs to the Buddhist literary tradition.