Kara (Hangul: kara, Japanese: kara, often stylized as KARA) was a South Korean pop girl group formed by DSP Media in 2007. The group's final lineup was composed of Park Gyuri, Han Seungyeon, Goo Hara and Heo Youngji. Members Nicole Jung and Kang Ji-young officially departed from the group in 2014, while Kim Sung-hee left in 2008. The group's name comes from the Greek word "chara" (khara, lit. "joy"), which they interpreted to mean "sweet melody".

The group was scheduled to have their comeback in March 2008 with their second album, however, member Kim Sung-hee suddenly announced that she would be leaving the group due to parental pressure because her participation in the group was contingent on the maintenance of her grades. In response, DSP stated that the second album that was recorded would be shelved and replaced by a mini-album to come in May; in addition, two members would join the group. Auditions were held, and the two new members were eventually revealed to be Goo Ha-ra and Kang Jiyoung. The group made their return in the music industry as a quintet on July 24, 2008 with "Rock U" on M! Countdown. They made their comeback with the "cute" and "playful" image which was the complete opposite of the group's original image from their debut. In the same month, their first mini-album titled Rock U was also released. The second season of Kara Self Camera was premiered on August 18, 2008, which chronicled how the group was adapting to their two new members.  On November 29, 2008, DSP released a teaser video for their upcoming single, "Pretty Girl", which received over 40,000 hits within 12 hours. The full video was released on December 2, 2008 online and was positively received by the public. The EP, Pretty Girl, was released on December 4, embodying a "fun-party" concept. The group began its comeback on all major music shows on December 4, 2008, starting with M! Countdown. During their first national performance on KBS's Music Bank, member Goo Hara accidentally gasped "ah!" live on air due to slipping on falling confetti, and reportedly cried profusely afterwards. The incident became a hot issue to many viewers, but Goo Hara received comfort instead of criticism from the general public.  Park Gyuri attributed their popularity increase to their "pretty but natural" appeal, while media reports gave credit to the band for finally finding its own identity in the music industry since the group's debut and to older male fans, most notably singer Shin Hae Chul. Due to their increasingly hectic schedule as their popularity rose, a few of the group's members were taken to the hospital on December 19 after a Music Bank rehearsal for cold symptoms and exhaustion.Answer this question using a quote from the following article:

What is "Rock U"
The group made their return in the music industry as a quintet on July 24, 2008 with "Rock U" on M! Countdown.