"Mamma Mia" featured the music of what pop group?

This is one of my favorite musicals. The story is fun, the acting is wonderful and the singing is fabulous. ABBA's music is beautiful.

why is the question expressed in the "past tense." Does the music no longer belong to ABBA?

They were such a beautiful group who created lovely songs and music, but sadly didn't last many years. Hearts were broken among them selves and it made the music lovers Hearts to feel broken as well.