通过这篇文章我们来看看主旨题，托福听力一定要听好开头，因为开头一定会出现与主旨相关的关键词，有的时候还起着总领全文的作用。
我们先来看一下文章的整体结构：
首先开头通过类比引出主旨—One discovery changes understanding of civilization，接着举了一个例子，出现专有名字—Anti-kythera Mechanism，接着对其下定义和做描述介绍了它的features，然后解释这个Anti-kythera Mechanism是如何challenge people’sunderstanding。
了解了整体结构之后，我们来看这篇文章的主旨题。
6.What is the lecture mainly about? (D)
A.The methods archaeologists used to reconstruct the Antikythera Mechanism
B.The influence the Antikythera Mechanism has had on the study of physics
C.A research project in the combined fields of archaeology, physics, and mathematics
D.An archaeological discovery that challenged an accepted historical view
同学们很容易被文章的细节给吸引住，觉得应该选与AM这个专有名字有关的选项。但是，其实AM是个例子，这个例子的目的是为了说明一个archaeological find挑战了人们的认识。一定要注意文章的整体逻辑结构!
Iwas talking to one of my colleagues in the physics department the other day, and we ended up discussing how one discovery can change everything. My colleague mentioned how the theory of relativity completely changed the fieldof physics. At any rates, that conversation got methinking about archaeological finds that really changed our understanding of ancient civilizations. So I want to talk about the discovery of the Antikythera Mechanism.