A is the correct answer.
Rap and country music both are popular in United States. Both music have different origins, showing a mix of different cultures.
Cultural Diversity is basically the existence of different cultures within a single society. A country or a city having people from different cultures is said to be culturally diverse. Dubai is currently the most diverse city of the world at the moment.
So in this question, it is said that two music genre are equally popular in United States. Both have different origins but are praised equally in a country. Thus making a good example of Cultural Diversity.