Question: Not Alone, is Zhang Liyin's which number overall single, Zhang held a showcase to support the release of the single, which was held at the Century Theater in Beijing, EXO members Tao and Chen were guests, Exois a South Korean-Chinese boy group based in Seoul? 
Context: Exo (Korean: 엑소 ; stylized as EXO) is a South Korean-Chinese boy group based in Seoul.  Formed by S.M. Entertainment in 2011, the group debuted in 2012 with twelve members separated into two subgroups, Exo-K (Suho, Baekhyun, Chanyeol, D.O., Kai, and Sehun) and Exo-M (Xiumin, Lay, Chen and former members Kris, Luhan and Tao ), performing music in Korean and Mandarin respectively.  Exo's first album "XOXO" (2013), which contained the breakthrough hit "Growl", was a critical and commercial success, winning both Disk Daesang at the 28th Golden Disk Awards and Album of the Year at the 15th Mnet Asian Music Awards.  It sold over one million copies, making Exo the best-selling Korean artist in twelve years.  Subsequent albums and EPs continued with strong sales, and Exo were ranked the most influential celebrity by "Forbes" Korea Power Celebrity for the years 2014 and 2015.  They have been named "the biggest boyband in the world" by media outlets. Huang Zitao (born 2 May 1993), better known as Tao, is a Chinese rapper, singer-songwriter and actor.  He is a former member of the South Korean-Chinese boy group EXO.  In 2015, he made his solo debut with the mini-album "T.A.O", under the new stage name Z.Tao. Agape is Zhang Liyin's third overall single, released on August 2, 2014 in China and August 6 in Korea.  The song is dedicated to the victims of the 2008 Sichuan earthquake.  Co-written by Zhang Liyin and Taiwanese lyricist , the song is about a mother who allows her child to live at the expense of her own life.  The single's B-side track "Back Then" is a cover of the title song from Taiwanese film "You Are the Apple of My Eye". The discography of the South Korean-Chinese boy band Exo consists of four studio albums, five extended plays, and twenty one singles. Exo was formed by the Korean entertainment company S.M. Entertainment in 2011, and formerly consisted of twelve members separated into two sub-groups, Exo-K and Exo-M, releasing the same music simultaneously in both Korean and Mandarin in South Korea and China, respectively.  The group's first release, the extended play "Mama", was released in April 2012.  The album topped Korean music charts on its release. Exo Planet #2 – The Exo'luxion is the second tour of South Korean-Chinese boy band EXO.  The tour began in Seoul's Olympic Gymnastics Arena on March 7, 2015.  The tour was officially announced in January 2015 with the first 5 dates in South Korea.  The tour had 39 dates throughout Asia and 5 dates in North America.  The tour gathered over 742,000 fans around the world, making it EXO's largest tour to date and one of the largest tours by a Korean act in recent history. Zhang Liyin (born February 28, 1989), better known in South Korea as Jang Ri-in, is a Chinese singer.  She is a former member of S.M. Entertainment's project group S.M.  The Ballad.  Subject to much publicity, Zhang was nicknamed the "Chinese BoA" and the next leader of the Korean Wave.  She speaks both Mandarin, which is her first language, and fluent Korean, and has released singles in both China and South Korea, singing in both languages. Zhang Yixing () (born (1991--) 07, 1991 ), better known by his stage name Lay (Korean: 레이 ), is a Chinese singer, songwriter, record producer, dancer, actor, model, author and voice actor.  He is a member and main dancer of the South Korean-Chinese boy group Exo and its sub-unit Exo-M.  He was first known after participating in the Chinese TV talent show "Star Academy" in 2005. Not Alone (我一个人) is Zhang Liyin's fourth overall single, released on August 20, 2014 in China and August 22 in South Korea.  The song is a remake of 'By Myself' (나 혼자서) from the SBS drama "Ja Myung Go" which "Girl's Generation" member Tiffany sang back in 2009.  Zhang Liyin had mentioned that the song is a follow up track and a continuation of the storyline of "Agape" during her YouTube Interview with Victoria and Tao.  In a press release from SM Entertainment on September 18, they announced that the song will be Zhang Liyin's fourth single.  It was released on September 20, 2014 in China through Baidu and then later released in South Korea through Korean music sites MelOn, Genie, Naver and Bugs on September 22.  Zhang held a showcase to support the release of the single, which was held at the Century Theater in Beijing.  EXO members Tao and Chen were guests at the said event. Kim Jong-dae (born September 21, 1992), better known by his stage name Chen, is a South Korean singer-songwriter and actor.  He is a member of the South Korean-Chinese boy group EXO and its sub-unit EXO-CBX, as well as S.M Entertainment's ballad group SM the Ballad. Exo Planet #3 – The EXO'rDIUM is the third tour of South Korean-Chinese boy band EXO.  The tour was officially announced on June 15, 2016 and began in Seoul's Olympic Gymnastics Arena on July 22, 2016.  The first 6 dates were in South Korea, making EXO the first K-pop group to have the longest solo concert series in Seoul.  During EXO's EXO'rDIUM tour, member Kai struggled with an ankle injury, making him unable to fully participate in the first three months of the tour.  In February 2017, official announcements were made to announce that promotions would continue in Mexico and the United States, marking the EXO'rDIUm tour as EXO's second World Tour.  It was announced on March 30, 2017 that the tour will conclude in Seoul with two encore performances on May 27 and 28, titled "Exo Planet #3 – The Exo'rdium[dot]".
Answer: fourth