大学英语：The new music was built out of materials already in existence

    43. The new music was built out of materials already in existence. P1
　　44. They freely took over elements from jazz, from American country music, and as time went on from even more diverse sources. P2
　　45. What developed was a music readily taking on various forms and capable of an almost limitless range of expression. P2
　　46. In studio recordings, new techniques made possible effects that not even an electronic band could produce live. P3
    47. Electronic amplifiers also made possible a fantastic increase in volume, the music becoming as loud and penetrating as the human ear could stand. P3
　　48. Often music was played out of doors, where nature provided the environment. P4
     49． The social and political transformation of a country is essential to the development of the society.
　　50． All theories originate from practice and in turn serve practice.