 Complete the following phrase:  Sigríður Beinteinsdóttir has participated five times as a member of a group in 1990 and 1992, as a solo artist in 1994, and as a background vocalist in 1991 and 2006. Hera Björk has participated four times as background vocalist in 2008, 2009 and 2015 and as solo artist in 2010. Stefán Hilmarsson has participated twice as a member of a group in 1988 and as a member of a duo 1991, as have Selma Björnsdóttir 