The Phonautograph eventually evolved into the Phonograph. Thomas Edison discovered in 1878 a way to record sound onto soft. Impressionable material such as tinfoil, lead or wax. However, it was not until 1887 that this discovery was used to record sound on a flat disc creating a medium that could be mass produced. Emile Berliner discovered that instead of tracing the stylus over a rotating... the resulting disc would then be...
首先这是一篇讲： the history of recorded music or even recorded sound，这不是introduction，但看这一段，这是一个关于“Phonautograph”，中心句一般是而且经常是第一句"The Phonautograph eventually evolved into the Phonograph."讲的是change into something else or the next step.
为什么？因为根据“eventually”，这个词的意思表示跟时间有关，正在发生的事情。而“evolved”这个词的意思就是 change into something better. 所以我们可以总结这一段讲述的是 the evolution of the change into Phonautograph, the next step from what came before. 接下来，我们只需要确定我们找论据中关键词去验证找的中心句到底对不对就好了！
往下看，TE这个人，TE 发现的什么，发现了一个record sound 的way，发现了不同的材料“tinfoil, lead or wax”都在支持“evolved”，还有1878和1887去支持我们上一句说的“ eventually”。
再往下看，看到“a flat disc”，creating a medium，之后还有EB, instead of something. 这都是在支持“evolved”。