Question: Girls' Generation-TTS (, also known as TTS, TaeTiSeo, or Girls' Generation-TaeTiSeo) is a subgroup of South Korean girl group Girls' Generation, formed by S.M. Entertainment in 2012, is composed of three Girls' Generation members: Taeyeon, Tiffany, and which South Korean singer and actress, known professionally as Seohyun, born in which year ?
Context: Tiffany Hwang (born Stephanie Young Hwang, better known by the mononym Tiffany) is a South Korea-based American singer.  Her discography consists of one extended play, ten singles (including eight as featured artist), and twelve soundtrack appearances.  She debuted as a member of South Korean girl group Girls' Generation under S.M. Entertainment in August 2007 and has since achieved immense popularity on the Asian music scene.  Tiffany is also a member of the Girls' Generation subgroup TTS and has recorded tracks for soundtracks for various television drama series and films. Kim Tae-yeon, better known by the mononym Taeyeon, is a South Korean singer.  Her discography consists of one studio album, two extended plays (EPs), twenty singles (including four as featured artist), and three promotional singles.  She debuted as a member of South Korean girl group Girls' Generation in August 2007 and initially gained some popularity as a singer upon recording soundtrack songs "If" for "Hong Gil Dong" and "Can You Hear Me" for "Beethoven Virus" (2008).  She subsequently established herself as one of the most renowned vocalist on the South Korean music scene with further soundtrack recordings, notably "I Love You" for "" (2010), "Missing You like Crazy" for "The King 2 Hearts", "Closer" for "To the Beautiful You" (2012), and "And One" for "That Winter, the Wind Blows" (2013), all of which managed to enter the top ten of South Korea's Gaon Digital Chart.  Apart from soundtrack recordings, Taeyeon has also recorded duets with other artists, most notably "Like a Star" with The One and "Different" with Kim Bum-soo, which peaked at numbers one and two on the Gaon Digital Chart, respectively. Kim Tae-yeon (born March 9, 1989), referred to as Taeyeon, is a South Korean singer.  She had been a trainee at S.M. Entertainment's Starlight Academy during her middle school years before debuting as a member of the agency's girl group, Girls' Generation, in 2007.  Since then, she has risen to prominence due to the group's success on the Asian music scene and further participated in the agency's projects Girls' Generation-TTS and SM the Ballad.  Aside from group activities, she has also recorded songs for various television dramas and movies. Girls' Generation-TTS (, also known as TTS, TaeTiSeo, or Girls' Generation-TaeTiSeo) is a subgroup of South Korean girl group Girls' Generation, formed by S.M. Entertainment in 2012.  It is composed of three Girls' Generation members: Taeyeon, Tiffany, and Seohyun.  The group has released three EPs: "Twinkle" (2012), "Holler" (2014), and "Dear Santa" (2015). Don't Say No is the debut extended play by South Korean singer Seohyun.  It was released by S.M. Entertainment on January 17, 2017.  The EP marked the official solo debut of Seohyun, who had been known as a member of South Korean girl group Girls' Generation for ten years. Girls' Generation-TTS (also known as TaeTiSeo) is a subunit of South Korean girl group Girls' Generation, consisting of members Taeyeon, Tiffany and Seohyun.  The subunit debuted in 2012 with the extended play "Twinkle", which peaked at number one on the Gaon Album Chart and has sold over 155,000 physical units.  The EP yielded a single of the same title, which peaked atop the Gaon Digital Chart and sold over 2.5 million digital units in 2012. Seo Ju-hyun (born June 28, 1991), known professionally as Seohyun, is a South Korean singer and actress.  She debuted as a member of girl group Girls' Generation (and later its subgroup TTS) in August 2007, who went on to be one of the best-selling artists in South Korea and one of South Korea's most popular girl groups worldwide.  Apart from her group's activities, she has established herself as an actress, notably through her participation in the original and Korean versions of stage musicals including "Moon Embracing the Sun", "Gone with the Wind" and "Mamma Mia".  She also starred in the drama "".  She debuted as a solo artist with her debut mini album, "Don't Say No", on January 17, 2017, making her the third Girls' Generation member to debut as a solo artist. This is the videography of the South Korean girl group Girls' Generation.  Girls' Generation have been in the music business ever since debuting in August 2007.  The group is composed of eight members: Taeyeon, Sunny, Tiffany, Hyoyeon, Yuri, Sooyoung, Yoona and Seohyun.  Former member Jessica was dismissed from the group in 2014. Girls' Generation (), also known as SNSD, is a South Korean girl group formed by S.M. Entertainment.  The group is composed of eight members: Taeyeon, Sunny, Tiffany, Hyoyeon, Yuri, Sooyoung, Yoona, and Seohyun.  Originally a nine-piece group (with Jessica, who later departed from the group in September 2014), Girls' Generation debuted in 2007 with their Korean eponymous debut album.  Though the album gained some attention, it was not until 2009 that the group rose to fame with the single "Gee", which claimed the top spot on KBS's "Music Bank" for a record-breaking nine consecutive weeks and was named the most popular song of the 2000s in South Korea by Melon.  Girls' Generation further consolidated their popularity on the South Korean music scene with follow-up singles "Tell Me Your Wish (Genie)", "Oh! ", and "Run Devil Run", which were released in mid-2009 and early 2010. Stephanie Young Hwang (born August 1, 1989), known professionally as Tiffany or Tiffany Hwang, is an American singer based in South Korea.  Born and raised in California, she was discovered by South Korean entertainment agency S.M. Entertainment at the age of fifteen and subsequently moved to South Korea.  After four years of training, Tiffany debuted as a member of girl group Girls' Generation (and later its subgroup TTS) in August 2007, who went on to be one of the best-selling artists in South Korea and one of South Korea's most popular girl groups worldwide.  In 2016, following her contribution to several side projects during the early part of her career, Tiffany became the second Girls' Generation member to release a solo debut album, "I Just Wanna Dance".
Answer: 1991