What explains the emergence of a national culture in the 1920s?

the growth of fundamentalism
the growth of the mass media
the programs of the new deal

The answer is the growth of the mass media.  1920s was called as the formation of modern American mass culture.  During the 1920s, the mass and consumer culture radio and motion pictures emerged and created a new era to the American culture.  This was the time of mass media like television and radio.

d. it gave farmers a way to organize for more political power