Question: Chou Tzu-yu is part of the girl group who debuted on October 20, 2015 with what EP?
Sentence (from "Twice (band)"): The group is composed of nine members: Nayeon, Jeongyeon, Momo, Sana, Jihyo, Mina, Dahyun, Chaeyoung, and Tzuyu.
Relevant evidence: No