Title: Baby (Justin Bieber song)
Content:  "Baby" is a song by Canadian singer Justin Bieber, alongside American rapper Ludacris. It was released as the lead single on Bieber's debut album, My World 2.0. The track was written by Bieber, Ludacris, Christina Milian, Tricky Stewart (who worked with Bieber on a previous single "One Time"), and R&B singer The-Dream, with production helmed by the latter two. It was available for digital download on January 18, 2010. The song received airplay directly after release, officially impacting mainstream and rhythmic radio on January 26, 2010. The song has received positive reviews from critics who complimented the song's effective lyrics and chorus and commended Ludacris' part and the song's 
Title: Baby (Justin Bieber song)
Content:  Bieber premiered an acoustic version of the song on MuchMusic. He sang the song on VH1's Pepsi Super Bowl Fan Jam, along with other performers Rihanna, JoJo and Timbaland, and on CBS' The Early Show as a part of their Super Bowl programming. He performed the song the first time with Ludacris on BET's SOS: Saving Ourselves – Help for Haiti Telethon, on February 6, 2009, which also aired on VH1, and MTV. During the chorus, he changed the lyrics to "Baby, baby, Haiti", to show support for the cause, and the reason everyone came together for the show. In the week of his album release, he performed the song on The View and 106 & Park. Bieber also performed the song at the 2010 Kids Choice Awards on March 27. Bieber performed the song along with 
Title: Baby (Justin Bieber song)
Content:  The song is predominantly upbeat, featuring Bieber's R&B vocals over a backdrop containing a dance infused beat, full of keyboard and "disco string" synths. The song is played at a tempo of 130 BPM and is composed in the key of E♭ major with Bieber's vocal range spanning from the low-note of G3 to the high-note of C5. According to Jody Rosen of Rolling Stone, the song "blends winks at Fifties doo-wop with hip-hop chants", comparing the style and the lyrics "My first love broke my heart for the first time/And I was like/Baby, baby, baby, ooooh/I thought you'd always be mine" to fifties ballads like "Tears on My Pillow", "Why Do Fools Fall in Love" and "Earth Angel". 
Title: Just a Baby Boy
Content:  "Just a Baby Boy" is a song by American rapper Snoop Dogg featuring guest vocals from American R&B singer and actor Tyrese and rapper Mr. Tan, taken from the soundtrack Baby Boy. The song was written by Snoop Dogg, Tyrese and Kevin "DJ Battlecat" Gilliam, who also handled production. The song was also included in the second Tyrese studio album, 2000 Watts.
Title: Baby (Justin Bieber song)
Content:  Nick Levine of Digital Spy felt the song was "no great departure from what he's given us before", but felt the production of Tricky and The-Dream helped give the song a "simple", "big" chorus about "puppy love" that works. Melanie Bertoldi of Billboard said, "The midtempo number's undeniably contagious chorus should keep Bieber's tween fan base satisfied, and Ludacris' brief cameo adds a welcome urban twist." Bertoli went on to say, "The matchup adds a layer of maturity to Bieber's repertoire and should further solidify his growing presence on the charts." Rap-Up magazine said that "the sweet pop fare gets a little street cred courtesy of the teen sensation's labelmate Ludacris." Jody Rosen of Rolling Stone appreciated the song's vintage doo-wop and fifties aesthetic and hip-hop chants, and said the song included "one of the catchiest choruses concocted by the-Dream and Tricky Stewart, the duo behind "Umbrella" and "Single Ladies." Luke O'Neill of Boston Globe had mixed thoughts about the song calling Ludacris' cameo "goofy", and said, the song "effects a musical anachronism, albeit a catchy one, but in this sped-up recycling moment all styles all at once are grist for the mill."
Title: Baby-Baby-Baby
Content:  "Baby-Baby-Baby" was written and produced by Babyface, L.A. Reid and Daryl Simmons. The song features lead vocals from Tionne "T-Boz" Watkins, with Rozonda "Chilli" Thomas adlibbing and singing the middle-8 sections. It is the first song not to contain a rap by Lisa "Left Eye" Lopes, who instead recorded a rap for the song's remix version. "Baby-Baby-Baby" was sampled by rapper Bow Wow for his single "You Can Get It All". Bow Wow's song was produced by Jermaine Dupri, who also appeared in the "Baby-Baby-Baby" video.
Title: Baby (Justin Bieber song)
Content:  Smile" on the eighteenth episode of season thirty five of Saturday Night Live. Bieber performed an acoustic rendition of the song along with a freestyle by good friend Drake at the 2010 Juno Awards. In April 2010, Bieber noted that due to his voice changing, he could no longer hit all the notes in "Baby", and for live performances, the key is lowered. Bieber performed the song live in Sydney, Australia on April 26, 2010, in the Sunrise studios after his public performance was cancelled. Bieber also performed the song on May 11, 2010, on The Oprah Winfrey Show. Bieber performed the song on June 4, 2010, on the Today Show along with "Never Say Never", "Somebody to Love", and "One Time". He performed the song with "Somebody to Love" at the 2010 MuchMusic Video Awards.
Title: Baby (Justin Bieber song)
Content:  new version of "The Way You Make Me Feel" saying, "..and the choreography does use a few of Jackson's less-suggestive moves." The MTV review goes on saying, "most of the video takes place in the bowling alley, there are also scenes of Bieber in other settings, hanging out with Luda, doing the moonwalk, messing with his hair and mugging for the camera. During the video Biebers friends and Villegas friends have several dance offs and Villegas eventually smiles at him. Regardless of his crush's apparent frustration with him, Bieber eventually wins her over. The video concludes with the pair walking off into the night holding hands." 
Title: Yummy (Justin Bieber song)
Content:  "Yummy" is a "straightforward R&B number" that moves along on pop-trap beats. Bieber's vocals span from F4 to the high B5. The song contains a "crisp bass line and plinking keyboards". Bieber rap-sings the pre-chorus, while he hits his "signature falsetto" in the bridge. Bryan Rolli of Forbes magazine called the chorus "seductive", albeit "meaningless". The song is considered an ode to Bieber's wife, Hailey Bieber.
Title: Baby (Fabolous song)
Content:  "Baby" is a song by American rapper Fabolous featuring Mike Shorey. It is the second single from Fabolous' third studio album Real Talk. The song reached #17 in the Hot Rap Tracks chart and #22 in the Billboard Hot R&B/Hip-Hop Singles & Tracks chart, although only managed #71 in the Billboard 100. The song failed to make a big impact on the UK Chart, where it missed out on the top 40 following its release. It contains a replay, not a sample of "I Can't Help It" by Michael Jackson, lyrics from "2 Bad" by Michael Jackson and of "Breakadawn" by De La Soul. (Replayed by J remy of Orange Factory Music) The chorus also samples "Big Poppa" by The Notorious B.I.G.. Rev Run makes a cameo appearance at the end of the music video.

Question: who sings the rap in baby by justin bieber?
Answer: Ludacris.