Question: On which channel did a television series air in 2015 that starred the main vocalist of the South Korean girl group Apink?

Context paragraphs:
Son Na-eun: Son Na-eun (born February 10, 1994) is a South Korean singer.  She is best known as a member of the South Korean girl group Apink.

Mr. Chu: "Mr. Chu" is a song by South Korean girl group Apink.  The song is their 5th Korean single and served as the lead single from their 4th mini-album "Pink Blossom".  It was released on March 31, 2014 by A Cube Entertainment.  The song composed by Duble Sidekick.  The song's music video was directed by Digipedi and released on the same day.  Apink performed the song for the first time on KBS's "Music Bank" on April 4.  The song peaked at number 2 on Billboard's K-Pop Hot 100.  Apink won six music show trophies for "Mr. Chu" and wrapped up promotions for Mr. Chu on May 25.  The song was the eighth best selling digital song in 2014, according to Gaon's year-end chart.  "Mr.Chu" was used for G9 TV commercial featuring Apink and comedian Lee Guk-Joo.  The Japanese version of "Mr. Chu" released as their second Japanese single on February 18, 2015.  On January 22, 2015 the short PV for "Mr. Chu" 'on-stage' Japanese version was released.

Apink discography: The following is the discography of South Korean girl group Apink, debuting in 2011.  The group consists of six members: Chorong, Bomi, Eunji, Naeun, Namjoo, and Hayoung.  Former member Yookyung left the group in April 2013.  The group has released three full-length albums and six extended plays, one special album, as well as two full-length Japanese albums.

Cheer Up! (TV series): Cheer Up!  (; lit. "  Sassy, Go Go") is a 2015 South Korean television series starring Jung Eun-ji, Lee Won-keun, Cha Hak-yeon, Ji Soo and Chae Soo-bin.  It aired from October 5, 2015 until November 10, 2015 on KBS2 every Monday and Tuesday at 22:00 KST for 12 episodes.

Yoon Bo-mi: Yoon Bo-mi (born August 13, 1993), better known by the mononym Bomi, is a South Korean singer, songwriter and actress.  She is best known as a member of the South Korean girl group Apink.

Park Cho-rong: Park Cho-rong (born March 3, 1991), better known mononymously as Chorong, is a South Korean singer-songwriter and actress.  She is best known as the leader of the South Korean girl group Apink.

Jung Eun-ji: Jung Eun-ji (born Jung Hye-rim, on August 18, 1993), better known by the mononym Eunji, is a South Korean singer, songwriter, actress and voice actress.  She is best known as the main vocalist of the South Korean girl group Apink.  Jung made her acting debut in the coming-of-age drama, "Reply 1997" in 2012.  She has since had roles in "That Winter, the Wind Blows" (2013), "Trot Lovers" (2014) "Cheer Up! " (2015), in addition to various voice acting roles.  She released her debut solo album, "Dream", in 2016.

Kim Nam-joo (singer): Kim Nam-joo (born April 15, 1995), better known by the mononym Namjoo, is a South Korean singer and actress.  She is best known as a member of the South Korean girl group Apink.

Pink Blossom: Pink Blossom is the fourth mini-album by South Korean girl group Apink, released on March 31, 2014.  Group leader, Chorong wrote two songs for the album.  A song "Mr.Chu", composed by Duble Sidekick chosen as the title song used to promote the album, with music video were released on the same day.  The song peaked at number 2 on "Billboard"'s K-Pop Hot 100.  Apink won six music show trophies for "Mr. Chu", and the song was the eighth best selling digital song in 2014, according to Gaon's year-end chart.  They released music video from another track of the album, "Crystal" on June 6.  The album was the second most selling album of the first week of release and end up at no 30 on 2014 Gaon Yearly Album chart by selling 66,139 albums, become the third highest album sales for girl group.

Oh Ha-young: Oh Ha-young (born July 19, 1996), better known by the mononym Hayoung, is a South Korean singer, songwriter and actress.  She is best known as a member of the South Korean girl group Apink.

Supporting paragraphs: Cheer Up! (TV series) Jung Eun-ji
Answer: KBS2