参考答案：B

解析：[听力原文] 21-25 We are rapidly nearing the end of this course in history of classical music. We have covered several centuries in a very short time. Much too short to do the music justice, of course, but then this is a survey course. From now until the end of this term, we will be talking about and listening to electronic music. You probably already know that it was in the 1950s that musical computers and synthesizers first appeared in universities. The first commercial synthesizers were sold about this time, too. The sophistication and complexity of these instruments has now increased to the point that they can produce almost any kind of sound. Some alarmists believe these new instruments will bring an end to classical music or that they already have. You know I don’t share this view, though I agree we are in the midst of revolution in instrument design. This, however, is not the first such revolution in musical history and probably not the last one either. Remember we’ve already studied the similar case in the early 19th century when the piano replaced the harpsichord and modern brass and wind instruments came into being. One of the most important reasons for the great popularity of electronic instruments is, of course, their relatively low price. Well, just look at it, only about 400 dollars for a piano. Naturally this has done a lot to increase sales for electronic instruments, expecting them to completely replace acoustic instruments.

[分析]： 主旨题。 本文开篇明示本次讲座的目的是From now until the end of this term，we will be talking about and listening to electronic music，然后作者围绕电子乐器的发展进行了全面的介绍，如电子乐器的起源、特点，人们对该类乐器的不同看法及该类乐器与传统乐器相比价格低廉等。总之，综合本文的主要内容可得出其主要内容与B项内容相符，因此该项为正确答案。[解题关键] 把握表示全文主旨的句式结构，如本文中from now until the end of this term，we will be talking about... 是解题的关键。