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?
Sentence (from "BBC Sessions 1968–1970"): BBC Sessions 1968–1970 is a 2011 studio compilation album featuring performances by the British hard rock band Deep Purple that were recorded at the BBC's Maida Vale Studios, London, and originally broadcast on various BBC Radio shows from 1968 through 1970.
Relevant evidence: Yes