Instruct: Classify Amazon reviews into positive or negative sentiment
Query: The opera pair of this half century.

the opera pairing of this half century, Di Stefano and Callas. Both had a dedication, and passion that has been unmatched. Callas the greatest singing actress of all time, and Di Stefano, whose unmatched beauty of voice is still talked about. Callas said of Di Stefano "He sang like a god." The only pairing of equal prestige was Caruso and Ponselle.