Question: Who sang background on the song En karusell when they were just 27 years old?

Context paragraphs:
Anni-Frid Lyngstad: Anni-Frid Synni, Princess Reuss of Plauen (German: "Anni-Frid Synni, Prinzessin Reuß von Plauen" ; born Anni-Frid Synni Lyngstad, 15 November 1945), commonly known as Frida Lyngstad, or just by the mononym, Frida, is a Norwegian-born Swedish singer, songwriter, and environmentalist.  Known for her warm personality, striking auburn hair and rich mezzo-soprano voice, she is best known as one of the lead singers of the Swedish pop band, ABBA.

Jimmy Reno: Jimmy Reno (born January 8, 1969) is a Southern Gospel singer from North Alabama.  Initially, he was a member of his family's singing group, and later a member of The Mystery Men Quartet and then Mark209.  While with Mark209, the group's first radio single, My Home In Heaven, a song that Reno was featured on, reached the top 45 on the Singing News national southern gospel music charts.  The single would remain on the national charts for 10 consecutive months.  In March 2012, Reno sang background vocals with Mark209 in concert for Country Music artist Ronnie Milsap.

Go Rest High on That Mountain: "Go Rest High on That Mountain" is a song written and recorded by American country music artist Vince Gill.  It was released in August 1995 as the sixth single from his album "When Love Finds You".  It is a eulogic ballad.  Gill began writing the song following the death of country music superstar Keith Whitley, who died in 1989.  Gill did not finish the song until a few years later following the death of his older brother Bob, in 1993, of a heart attack.  Ricky Skaggs and Patty Loveless both sang background vocals on the record.

Walking on the Chinese Wall: "Walking on the Chinese Wall" is a song written by Roxanne Seeman and Billie Hughes.  It was recorded by Philip Bailey and became the title track of his album "Chinese Wall".  Phil Collins produced, played drums and sang, as part of the backgrounds, on the song, however the song was not credited as a Bailey and Collins duet.  The Phenix Horns and additional overdub recording took place in Los Angeles, with George Massenburg engineering and mixing.  Josie James also sang background vocals on the song.

Rhythm &amp; Blues (Robert Palmer album): Rhythm & Blues is the thirteenth studio album by the British musician Robert Palmer.  His thirteenth solo studio album, it was released in 1999 and was his first new release in 5 years.  The album reached No. 118 in the UK but did not chart in the US.  Palmer's long-term girlfriend Mary Ambrose sang background vocals on some tracks, as did Sharon O'Neill who co-wrote "True Love".

Mae Moore: Moore studied art before moving to British Columbia to pursue music.  Her first hit came by co-writing the song "Heaven in Your Eyes" (with John Dexter), which would later be recorded by Loverboy for the "Top Gun" soundtrack in 1986.  She then worked with Barney Bentall and Colin Nairne from the band Barney Bentall and the Legendary Hearts, providing background vocals on their self-titled 1988 album "Barney Bentall and the Legendary Hearts".  She sang background vocals on and appeared in the music video for the Legendary Heart's "She's My Inspiration" song from that album.  Her association with Bentall and Nairne paid off, as CBS Records in Canada soon awarded her a recording contract.

Against the Wind (Bob Seger song): "Against the Wind" is a song by Bob Seger & The Silver Bullet Band from the 1980 album "Against the Wind".  "Against the Wind" is the highest ranking single from the album, peaking at number 5.  Glenn Frey of the Eagles sang background vocals on this song.

There's More Where That Came From: There's More Where That Came From is the sixth studio album by Lee Ann Womack, released in 2005.  It received numerous awards and critical acclaim and was also Womack's highest selling album since 2000's "I Hope You Dance".  The album was Womack's return to a traditional country music style, producing three charting singles between 2004 and 2006: "I May Hate Myself in the Morning", "He Oughta Know That by Now" and "Twenty Years and Two Husbands Ago", which peaked at numbers 10, 22, and 32, respectively, on the Hot Country Songs charts.  Womack's ex-husband, Jason Sellers, sang background vocals on "I May Hate Myself in the Morning".

En karusell: "En karusell" was originally released in 1972 as a 7" single in Sweden which was sung in Swedish and also in Japan where the song was titled "En Carousel" and sung in English.  The song was included as the A-side song and was credited to Björn & Benny.  Future members of ABBA Agnetha Fältskog and Anni-Frid Lyngstad did backing vocals on the song but were not credited for their contribution.The B-side song on the Swedish release was titled "Att finnas till" and the B-side song on the Japanese release was titled "Lycka".

Nearly Human: Nearly Human is a 1989 album by rock musician Todd Rundgren, released by Warner Bros.  Records.  It was his first release in four years, although he had been active as a producer in the intervening years.  Many of the album's songs deal with loss, self-doubt, jealousy, and spiritual recovery.  It was also the first collaboration between Rundgren and Michele Gray, a singer and ex-model who helped organize the sessions.  Gray sang background vocals, both on the record and on subsequent tours, and the pair later married.

Supporting paragraphs: En karusell Anni-Frid Lyngstad
Answer: Anni-Frid Lyngstad