Question: Who sings in the band Tokio Hotel, Bill Kaulitz, Cristina Scabbia or both?

Context paragraphs:
Bill Kaulitz: Bill Kaulitz (born September 1, 1989), also known mononymously as Billy (stylized as BILLY) for his solo act, is a German singer, songwriter, voice actor, designer, and model.  He is best known for his work from 2001 to the present as the lead singer of the band Tokio Hotel.

Rette mich (Tokio Hotel song): "Rette mich" (English: Rescue Me ), the third single by German rock band Tokio Hotel, first appeared on the band's 2005 album "Schrei".  The single version of "Rette mich", re-recorded as lead singer Bill Kaulitz's voice began to deepen, formed part of the "Schrei - so laut du kannst" release.  The band later recorded an English-language version of the song, entitled "Rescue Me", for their third studio album "Scream".

Cristina Scabbia: Cristina Adriana Chiara Scabbia (] ; born 6 June 1972) is an Italian singer and lyricist, best known as one of the two vocalists in the Italian Gothic metal band Lacuna Coil.  She used to write an advice column in the popular rock magazine "Revolver", alongside musician Vinnie Paul.  Scabbia is featured in a Megadeth song "À Tout le Monde (Set Me Free)".  She also featured on "The Theory of Everything", an album from Arjen Anthony Lucassen's Ayreon project, with which she is cast as the Mother.  She is also the featured artist in the Apocalyptica song "S.O.S. (Anything But Love)" and another version of the Alter Bridge song "Watch Over You".  Her highest note ever hit is claimed to be an A7.  Scabbia performed a duet with the Italian ex-singer of Linea 77 Emiliano Audisio on the track "Beautiful Lie" to be part of the soundtrack for the 2013 Italian film "Passione sinistra".

Run Run Run (Tokio Hotel song): Run Run Run is a song originally written by Joacim Persson, Ry Cuming, and David Jost, recorded by the German recording band Tokio Hotel and American recording artist Kelly Clarkson featuring John Legend in separate versions for their respective studio albums "Kings of Suburbia" (2014) and "Piece by Piece" (2015).  Produced by Tom Kaulitz and Bill Kaulitz, and Persson; with additional writing by Bill Kaulitz, Tom Kaulitz, and Johan Alkenas, Tokio Hotel released their version as the first promotional single from "Kings of Suburbia" on 12 September 2014.  Clarkson later released her version, produced by Jason Halbert with additional writing by Tim James and Antonina Armato of the musical duo Rock Mafia, as the third promotional single from "Piece by Piece" on February 25, 2015.

I'm Not OK: I'm Not OK is the debut EP by the German rock band Tokio Hotel's lead singer, Bill Kaulitz , and was released through iTunes on May 20, 2016 under the moniker Billy.  It contains 5 songs.  The official artwork was designed by German designer Andrew Brawl, who is also a good friend of Billy.  The EP leaked on the Internet in April, nearly a month before official release due to iTunes music releasing system issues.

Tokio Hotel TV – Caught on Camera: Tokio Hotel TV – Caught on Camera is a DVD released by the German band Tokio Hotel on 9 December 2008.  It provides an exclusive behind the scenes view of the Tokio Hotel's Concerts and the very best of Tokio Hotel TV.

Der letzte Tag (Tokio Hotel song): "Der letzte Tag" (English: The Last Day ) is the fourth single by German alternative rock band Tokio Hotel.  Although the song appears on the band's 2005 debut album "Schrei", the single version involved a re-recording, because singer Bill Kaulitz's voice broke after the release of the album.  The re-recording, along with a new song called ""Wir schliessen uns ein"" and a B-side, ""Frei im freien fall"", appear on Part 1 of this single, and on some copies of the re-released and expanded "Schrei" album "Schrei - so laut du kannst".  The song was later translated into English for their "Scream" album, and called "Final Day".  It was not released as an English single.

Tokio Hotel discography: The discography of Tokio Hotel, a German rock group, consists of four studio albums, two live albums, one EP, one compilation album, seventeen singles, twenty-one music videos, and five video albums.  Tokio Hotel was formed in 2001 in Magdeburg, Germany, by singer Bill Kaulitz, guitarist Tom Kaulitz, drummer Gustav Schäfer and bassist Georg Listing.  The group's debut single, "Durch den Monsun", entered the German singles chart at Number 15 on 20 August 2005, and reached Number 1 the following week.  It also reached Number 1 on the Austrian singles chart.  It was followed up with the single "Schrei", which failed to match the success of "Durch den Monsun"; its highest chart position was Number 3 in Austria.  The band released their debut album, "Schrei", on 19 September 2005.  It topped the charts in Germany and Austria, and was certified Platinum by the German and Austrian affiliates of the International Federation of the Phonographic Industry (IFPI) and by the Syndicat National de l'Édition Phonographique (SNEP) in France.  In 2006, a third and fourth single, "Rette mich" and "Der letzte Tag", were released; both reached Number 1 in Germany and Austria.  The lead single from Tokio Hotel's second album, "Zimmer 483", was "Übers Ende der Welt", released on 26 January 2007.  It became Tokio Hotel's fourth single to have reached Number 1 on the German and Austrian charts.  "Zimmer 483" was released on 23 February 2007, and reached the top spot on the German albums chart.  The album's second single, "Spring nicht", was released on 7 April, charting at Number 3 in Germany, 7 in Austria, and 21 in Switzerland.  "Zimmer 483" was certified gold in three countries.

Loitsche: Loitsche is a village and a former municipality in the Börde district in Sachsen-Anhalt, Germany.  Since 1 January 2010, it is part of the municipality Loitsche-Heinrichsberg.  This is where Tokio Hotel singer Bill Kaulitz and guitarist Tom Kaulitz grew up.

Tokio Hotel: Tokio Hotel is a German rock band, founded in 2001 by singer Bill Kaulitz, guitarist Tom Kaulitz, drummer Gustav Schäfer, and bassist Georg Listing.  Their sound encompasses multiple genres, including pop rock, alternative rock, and electropop.  The quartet have scored four number-one singles and have released three number one-albums in their native country.  The band has sold more than 10 million CDs worldwide.

Supporting paragraphs: Bill Kaulitz Cristina Scabbia
Answer: Bill Kaulitz