問：1. Q: What is Secret?
答： A: Secret is a South Korean girl group formed by TS Entertainment in 2009.
問：6. Q: What is Secret's most popular song?
答： A: Secret's most popular song is "Poison," which was released in 2014 and became a huge hit in South Korea.
問：9. Q: What is the reason behind Song Ji-eun's departure from Secret?
答： A: Song Ji-eun left Secret in 2014 to focus on her solo career and acting.
