Question: Who was the English conductor and Director of Music for the British Broadcasting Corporation, who first performed Ralph Vaughan William's Symphony No. 6?
Sentence (from "Symphony No. 6 (Vaughan Williams)"): Within a year it had received some 100 performances, including the U.S. premiere by the Boston Symphony Orchestra under Serge Koussevitzky on 7 August 1948.
Relevant evidence: No