As far as I know, this is a type of music popular in the 1950s, a(n) of jazz and folk music.
A. mixture
B. tradition
C. practice
D. invention
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(答案→)A. mixture
B. tradition
C. practice
D. invention
解析：考查名词辨析。A混合物；B传统；C锻炼，做法；D发明；句意：据我所知。这是一种在20世纪50年代很流行的音乐，一种爵士乐和民间音乐的混合音乐。