The answer is A, failure of the Treat of Versailles. That was in the end of World War I.
To keep the war away from the US
and
To protect their families
Bill Monroe is a great musician. He also knows how to play a mandolin. Through writing a song, he made a new genre of music called bluegrass. As most of the people would tag him as the father of blueggrass. His family, mother and brother loves to play music, so no wonder , even though Bill was still a child, he loved music and inclined to it.
It was during the Great Depression.