18. Rap music first appeared in New York in the 1970s. Later, it spread to large cities with
vibrant African-American populations (such as LA, Oakland, Detroit, Chicago) without
being absorbed by the smaller cities and rural areas in between. This type of spatial
diffusion is called
A) relocation potential
B) hierarchical diffusion
C) contagious diffusion
D) cultural diffusion
E) cascade diffusion