题目内容：
Which of the following statements is true，according to the research findings reposed in paragraph 6?
A．Repeated hearings of complex pieces of music are enjoyable and not tiresom B．Repeated hearings of complex pieces of music are tiresome at first and then become enjoyabl
C．Repeated hearings of simple songs are more enjoyable than those of complex pieces of musi
D．Repeated hearings of simple songs become tiresome sooner than those of complex pieces of musi
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