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Two 's Company The Duets is a 2006 studio album by Cliff Richard featuring various duet s he has recorded with other recording artists , including Elton John , Barry Gibb , Dionne Warwick , Olivia Newton-John and Lulu .
 Cliff Richard, Elton John, Barry Gibb, Dionne Warwick, Olivia Newton-John, Lulu
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Cliff Richard, Elton John, Barry Gibb, Dionne Warwick, Olivia Newton-John, Lulu