题干分析：讲座主要内容。

原文定位：

So in our last class, we looked at Bronze Age trade routes. And remember when we say Bronze Age, we're talking about the period from about 5000 years ago until about 2500 years ago. And when we discussed trade routes, we looked solely at land routes. Today, we'll concentrate on sea routes. And first, I want to talk about a shipwreck.

选项分析：考察文章整体内容的把握。文章开头提到之前在讲青铜时代的贸易路线，并且主要讲的是陆上商路，接下来今天要讲的是海上商路，在其中又首先要讲的是一艘沉船；之后整篇文章都在讲从这篇沉船上得出了关于青铜时代海上商路的各个结论，可知应选择C选项。A选项只占文章篇幅的一小部分，也不是文章开头给出的内容；B、D选项均未提及。