This is driving me crazy

Peggy Wood's singing voice is dubbed by Margery MacKay, the wife of the rehearsal pianist Harper MacKay, as Wood was not able to sing the high notes of the song. Rodgers wrote the piece in the key of C, with a modulation towards the end of the piece into the key of D flat, making the last note that the Mother Abbess sings an A flat (Ab5), though in the film it was sung a tone lower. With the popularity of the stage play it would seem Peggy Wood was not alone. Given the range of the piece and the average age of the actor playing Mother Abbess, the oldest character in the story, the song has proven daunting for many actresses over the years.