The Key to Perfection is a promo album by Swiss electronic duo Yello, released on September 4, 2012.
 It was not released on a label, and was distributed by Volkswagen officials at special events.
 The record contains additional vocals by Billy Mackenzie (on track 3), Heidi Happy (on track 4), and Malia (on track 7).
Billy MacKenzie (born 7 April 1984 in Edinburgh) is a Scottish professional motocross racer.
"Say" is a song recorded by English band The Creatures (aka singer Siouxsie Sioux and drummer Budgie).
 It was co-produced by Steve Levine.
 The song is about the suicide of Billy Mackenzie of Associates.
Chain was Edinburgh musician Paul Haig's third album and was released in May 1989 on Circa Records, a subsidiary of Virgin Records.
 "Chain", which Haig financed himself, was recorded and completed in 1988, but it sat on the shelf after the normally accommodating Les Disques Du Crepuscule decided not to take up the option of releasing it.
 The album was co-produced by long-time Haig cohort, Alan Rankine, instrumentalist with celebrated Dundee band, The Associates.
 There was another Associates connection on the album - the track "Chained" was written by Haig's good friend, Billy Mackenzie.
 Haig returned the favour and gave Mackenzie the track "Reach The Top" for his album "The Glamour Chase", which after many years in limbo was finally released in 2002.
William MacArthur "Billy" MacKenzie (27 March 1957 – 22 January 1997) was a Scottish singer, with a distinctive high tenor voice; he was best known as a member of The Associates.
Jessica & Krystal is an OnStyle variety TV show starring Korean American sisters Jessica Jung, former member of Girls' Generation and Krystal Jung of f(x).
"The Rhythm Divine" is a 1987 song by Boris Blank, Dieter Meier, and Billy Mackenzie.
One Second is Yello's fifth original studio album, having been preceded by a 'new mix' compilation the previous year.
 Released in 1987, the album is noteworthy for featuring both Billy MacKenzie and Shirley Bassey, the latter singing vocals on "The Rhythm Divine".
Jessica Jung (born April 18, 1989), known professionally as Jessica, is an American singer, songwriter, actress, model, fashion designer, and businesswoman currently based in South Korea.
 Jung was born and raised in San Francisco, California.
 At the age of eleven, she was discovered by South Korean entertainment agency S.M. Entertainment and subsequently moved to South Korea.
 In 2007, Jung debuted as a member of the South Korean girl group Girls' Generation.
 The group later became one of the best-selling artists in South Korea, and one of South Korea's most popular girl groups nationwide and worldwide.
Alan Rankine (born 17 May 1958) is a Scottish musician and record producer best known as keyboardist/guitarist for the rock band Associates, which he co-founded with Billy Mackenzie in the late 1970s.

Question: Billy Mackenzie and Jessica Jung, have which occupation in common?
Answer: singer