Who helped to grow the repertoire of concert band music?

The correct answer highlights the contributions of Boosey and Company, and Chappell, as significant publishers and advocates for concert band music. These companies played a crucial role in expanding the repertoire by actively commissioning new works, publishing a wide array of compositions, and promoting existing repertoire. Their efforts helped to shape the concert band literature, making a variety of styles and genres more accessible to conductors and performers, which in turn enriched the concert band experience.

While other options like Oxford University Press, Schirmer, and Hal Leonard have made valuable contributions to music publishing, Boosey and Company and Chappell are particularly noted for their focused impact on concert band music specifically, particularly in the 20th century. Their dedication to advancing concert band compositions helped elevate the medium and encouraged composers to write for this ensemble, thereby expanding the repertoire in a meaningful way.