Question: Which band along with two other British bands is referred to as the "unholy trinity of British hard rock and heavy metal in the early to mid-seventies" whose performance was featured in a 2011 studio compilation album at the BBC's Maida Vale Studios?
Facts:
BBC Sessions 1968–1970 is a 2011 studio compilation album
BBC Sessions 1968–1970 was recorded at the BBC's Maida Vale Studios
BBC Sessions 1968–1970 featured performances from Deep Purple
Deep Purple together with Led Zeppelin and Black Sabbath are referred to as the "unholy trinity of British hard rock and heavy metal in the early to mid-seventies"
Answer: Deep Purple