大部分的語段都是由三個部分組成的：主旨句、擴展句和結尾句，主旨句用來點出語段的主題思想。找到語段主旨句后，就可與題目選項進行匹配，快速獲取正確答案。下面我們通過兩道托福聽力真題解析，來具體看看如何利用語段主旨句幫助我們解題。

真題1
According to the professor, how is old computing different from new computing?
A. Old computing cannot be used to create complex programs.
B. Old computing tries to accommodate more types of users.
C. Old computing concentrates less on the needs of users.
D. Old computing focuses less on marking fast computers.
【聽力原文】
Ok, so it’s really important to find out what people want, what’s useful to them, before we develop new technologies, which brings me to the next point about new computing: that designs should be not only useful, but also user-friendly. Besides usefulness, usability is important. The idea that computer programs, accessories, websites, really anything related to your computer should be easy to use. Sounds simple, I know. The term user-friendly has been around for years. The problem is we don’t always create things that are easy for users to use. Take websites: many of you have probably been on websites that were really confusing. You couldn’t find the information you were looking for or there was so much information on the site that you just gave up. Again, this is where thinking like da Vinci can help. The goal is to solve problems, not create new ones. Those websites might be really easy for their designers to navigate, but they aren’t the ones who need to use the sites. So again, designers need to involve the users from the beginning to find out their expectations and what kind of tasks they want to perform.
【答案解析】正確答案為C.
如上所述，該語段的主旨句為第一句話，即新的計算機設計注重客戶需求，正好對應C選項：Old computing concentrates less on the needs of users. 傳統的計算機設計不太注重客戶需求。

真題2
According to the professor, what determines the temperature of the barriers in the facility’s basements?
A. The amount of heat generated by the facility’s solar panels
B. The amount of heat transferred from the facility’s windows
C. The temperature of air drawn in from other locations
D. The temperature of the surrounding soil
【聽力原文】
And it only gets better! You see under each of the buildings, architects designed a broad, shallow basement space that’s kind of like a maze. Air, either from within the building or from the outside, is pulled into the basement space through air ducts and then forced to move slowly around concrete barriers. The air is sort of guided through the maze. Now these concrete barriers, they absorb heat from the air if the air is warm or if the air is cold, the cold is absorbed into the concrete, so it could be either way. Let’s say it’s hot air; hot waste air being pulled in from the computer rooms, say. Well, that air moves slowly back and forth around these barriers. In this particular situation then, the heat from the incoming air is transferred to the concrete, which then holds onto it, storing the heat until later when it’s slowly released throughout the building. That’s the concept of thermal mass in a nutshell.
【答案解析】正確答案為C.
該語段的主旨句是最后兩句。大意是空氣中的熱量被混凝土所吸收并儲存起來，隨后慢慢地將熱量釋放到建筑物內。正好對應C選項：The temperature of air drawn in from other locations 。