Possible Clues:

• The Magi, e.g.
• Group with three singers
• Nirvana, e.g
• Troika
• Charlie's Angels, e.g.
• Wynken, Blynken and Nod, e.g.
• Chamber group
• Destiny's Child, for one
• Crosby, Stills & Nash, e.g
• The Police, e.g