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 two-disc set collecting all the surviving sessions in the BBC archives.
Relevant evidence: No