Final answer:
After World War II, an accurate statement is that rock and roll emerged as a new genre of music. It was born from rhythm and blues, amplified and popularized by African-American and white musicians like Elvis Presley, leading to its association with youthful rebellion.
Step-by-step explanation:
An accurate statement about the changes in popular music after World War II is C) Rock and roll emerged as a new genre. This genre was born from the fusion of rhythm and blues with amplifiers and electronics, primarily advanced by African-American musicians. Rock and roll not only provided an escape from the standardized culture of affluent white America but also marked a form of rebellion among the youth. White musicians like Elvis Presley played a significant role in popularizing the genre, leading to its widespread acceptance and association with youthful rebellion and defiance of societal norms.
Moreover, the genre became a unifying force between predominantly white suburbs and black American music, albeit mainly through radio and record sales. By the end of the 1950s, 600 million rock albums had been produced, and though it faced resistance from some quarters, rock and roll had certainly left an indelible mark on the decade and on American popular culture.