The first country artists to be widely known achieved popularity in the late 1920s. The music of these performers was heard throughout tile south during the 1920s and 30s on radio programs.
By the 1950s, country music had become a significant force in pop music. Regular appearances on the radio show made stars of many performers. The singer-songwriter Hank Williams wrote four million-seller songs in 1950, seven in 1951, and four more in 1953.
By the 1970s, "some country musicians began combining country music with electric instruments, creating a country rock sound.
What does "Both styles" in Line 3, Paragraph 1 refer to？

A. Country music style. and the musical style. of the Southeastern states.
B. The musical styles of the Southwestern states and the Southeastern states.
C. The Southwestern musical style. and Texas musical style.
D. The styles of blues and the black rural dance music.