Question: The three-member South Korean boy band, High4, released in 2014 a song they collaborated with which South Korean singer, songwriter and actress who signed with LOEN Entertainment in 2007?

Context paragraphs:
A Flower Bookmark: A Flower Bookmark () is the first cover extended play by South Korean singer, songwriter, and actress IU.  It is also her sixth Korean-language mini-album.  The EP was released on May 16, 2014, the singer's birthday, by LOEN Entertainment under its imprint LOEN Tree.  Unlike her previous works, "A Flower Bookmark" features cover versions of nostalgic K-pop songs popularized from 1980s to 1990s.

Let It Go (Heo Young-saeng EP): Let It Go is the solo mini album debut of South Korean singer Heo Young-saeng of boy band SS501.  The EP of Korean-language songs was released on May 12, 2011 under B2M Entertainment and distributed by LOEN Entertainment.  The album was released in Taiwan on July 1, 2011 under Warner Music Taiwan.

Meet Me Again: Meet Me Again is the second Korean solo mini album of Kim Kyu-jong of South Korean boy band SS501.  It was released as a limited edition on July 18, 2012 by B2M Entertainment and distributed by LOEN Entertainment.  The album was released in Taiwan by Warner Music Taiwan on August 17, 2012 with a bonus DVD.

BTL (band): BTL (Korean: 비티엘 ; stylized as "BTL"), also known as Beyond The Limit, was a South Korean boy band signed under Kiroy Company.  The group consisted of nine members: Jisu, Jean.Paul, Jay, Robin, DoKa, Q.L, Max, Allen, and YuA.  They released their debut single "Too-G" (투지; Tuji ) on May 15, 2014 under LOEN Entertainment.  They were scheduled to release their second title song "Gold Moon" in the like-titled mini-album on July 23, 2015, but the mini-album was only released as a promotional album in Hong Kong.

High4: High4 (hangul: 하이포; stylized as HIGH4) is a three-member South Korean boy band under the management of N.A.P Entertainment.  The group currently consists of members Alex, Myunghan, and Youngjun.  They officially debuted into the Korean entertainment industry on April 8, 2014 with the song "Not Spring, Love, or Cherry Blossoms" featuring IU.  On January 31, 2017, it was announced that leader Sunggu would be leaving the group.

History (band): History (Korean: 히스토리 ) was a South Korean boy group formed by LOEN Entertainment in 2013.  They debuted on April 26, 2013 with "Dreamer", featuring the narration of their labelmate IU.  They were LOEN Entertainment's first boy group.  They officially disbanded on May 12, 2017.

IU (singer): Lee Ji-eun (Korean: 이지은 ; born May 16, 1993), better known by her stage name IU (Korean: 아이유 ), is a South Korean singer, songwriter and actress.  While still in middle school, IU auditioned for various talent agencies with ambitions of becoming a singer.  She signed with LOEN Entertainment in 2007 as a trainee and began her music career at the age of 15 with her debut album, "Lost and Found".  Her follow-up albums, "Growing Up" and "IU...IM", brought her mainstream success, but it was through "Good Day" (Korean: 좋은 날 ), the lead single from her 2010 album "Real", that she achieved national stardom.  "Good Day" spent five consecutive weeks at the top position of South Korea's Gaon Digital Chart and holds the record for spending the most number of weeks at No. 1 along with Psy's "Gangnam Style".

Bohemian (band): Bohemian (Korean: 보헤미안 , Japanese: ボヘミアン; stylized as BOHEMIAN), is a three-member South Korean pop/ballad group, that along with group endeavors, has recorded many soundtracks, abbreviated as OSTs, for South Korean films and Korean drama or k-drama for television in South Korea, as individual artists.  The group is composed of (Korean: 박상우 ), (Korean: 김용진 ), and Yoo Kyu Sang (Korean: 유규상 ).  Bohemian debuted in 2010 with members Park Sang Woo and Yoo Kyu Sang.  In 2012, they were joined by Kim Yong Jin.  The group is managed by HMG Entertainment, with recordings released by their distribution company, LOEN Entertainment.  Through a LOEN Entertainment agreement with Viki, a video streaming site, both Kim Yong Jin and Bohemian are listed as artists, and their music videos can be viewed.

Not Alone (Park Jung-min song): Not Alone is the debut Korean solo single of Park Jung-min of South Korean boy band SS501.  It was released on 20 January 2011 by CNr Media and distributed by LOEN Entertainment.  The single album was originally planned to be released on 25 November 2010, but due to the rising tensions between South Korea and North Korea, Park and his company decided to push back his album release and promotions to the beginning of 2011.

Turn Me On (Kim Kyu-jong EP): Turn Me On is the Korean solo mini album debut of Kim Kyu-jong of South Korean boy band SS501.  It was released on September 27, 2011 under B2M Entertainment and distributed by LOEN Entertainment.  On October 28, the album was also released in Taiwan by Warner Music Taiwan.

Supporting paragraphs: High4 IU (singer)
Answer: IU