一般来说，第四题阅读文章的题目就是问题中需要解释的学术概念，所以一个大原则就是，在文中找到原词重现，原词重现的那句话，有很大几率就是概念的定义。例如TPO4 target marketing：
Target Marketing
Advertisers in the past have used radio and television in an attempt to provide information about their products to large, general audiences; it was once thought that the best way to sell a product was to advertise it to as many people as possible. However, more recent trends in advertising have turned toward target marketing. Target marketing is the strategy of advertising to smaller, very specific audiences – audiences that have been determined to have the greatest need or desire for the product being marketed.Target marketing has proved to be very effective in reaching potential customers.
这里文章中出现了两次target marketing，第一句里说“最近更倾向于使用target marketing”，显然不是定义，那么第二句中“target marketing是一种广告策略……”就是概念的定义了。这种是最简单的，可以直接抄原句。
第二种，仍然是找到原词重现的那句话，但是要稍作改变，因为一句话摘抄出来之后，脱离了上下文，可能会出现意思表达不清楚的地方，如TPO25 cultural lag：
Cultural Lag
Technological change occurs very rapidly in modern society – sometimes more rapidly than many people are prepared for. As a result, when new technology emerges, people may struggle for a time to adapt to it. This period of transition, when people are adjusting to technological change, is known as cultural lag. At first, people are not accustomed to the new technology and may not understand it; they may therefore have a negative attitude toward it. Over time, however, their attitudes change, and they successfully incorporate the new technology into their daily lives.
这里this period of transition显然适合上文有联系的，“这个”如果离开了原文就不知道是哪个。在说的时候需要换成定冠词，变成Cultural lag refers to the period of transition during which people adjust to technological change.
其实这个还不是特别明显，因为就算是我们不做任何改变，直接摘抄原句，也只是有一些语法上的不通顺，但是并不影响听者对于概念的理解。那么我们再来看下一个，TPO33 carrying capacity :
Carrying Capacity
An animal species needs to have enough resources, like food and water, to survive in any given environment. However, because resources are limited, only a certain number of animals of a particular species are able to survive in a given habitat. The greatest number a habitat can support is known as the carrying capacity.If nothing happens to disrupt or unbalance the relationship between the animal and its habitat, the carrying capacity will remain stable. However, a carrying capacity is not fixed. If there is a significant disruption, such as an environmental event that alters the amount of available resources in the habitat, the carrying capacity will change.
这个不难看出，原词重现的句子就是定义，但如果照抄原句，会给人造成理解的困难，因为“the greatest number”在失去了前文的对于栖息地和动物数量的铺垫之后，就不知道是什么东西的最大数量，所以这里必须要补充好“the greatest number of a certain animal species”，听者才能明白在谈什么。
第三种，迷惑性比较大，就是出现原词重现的句子经常会被错认为是定义，但实际上它并不是定义，这种情况下，定义通常在离这句话比较近的一个句子里。例如TPO1 groupthink :
Groupthink
One process by which groups may make bad or irrational decisions is known as groupthink. Individual members of a group attempt to conform their opinions to what they believe to be the group consensus even though the result may be negative. There are many reasons why groupthink happens. These include the desire to be liked, fear of losing a job, or even not wanting to be the one employee delaying a decision that seems inevitable. These kinds of implicit pressures to conform lead group members to ultimately make decisions that each, by himself or herself, might normally not make.
这个文章中第一句话末尾“…… is know as groupthink.”使很多人认为这一句就是定义句。而是事实，如果我们把这句话做一下句子简化，会发现最后得到的信息是“groupthink is a process.”它是一种过程，并且由于这个过程，一个团队会做不好的决定，这里只说了后果，但是groupthink到底是怎样发生的，这个过程究竟是什么，我们并不知道，所以这句话并不是定义。而真正的定义在它后面的一句“Individual members of a group attempt to conform their opinions to what they believe to be the group consensus even though the result may be negative.”这句话解释了，人们会使他们自己的想法，和他们认为团队里其他大多数人的想法保持一致，这样才可能会产生坏的结果，这句话才解释了groupthink到底是怎样的一个过程，所以它才是定义。
我们再来看一个例子，TPO24，flagship species：
Flagship Species
Environmental organizations work to protect plants and animals whose natural habitats are threatened by human activity. One way they do this is by selecting a particular species to represent the threatened habitat to the general public. This species, called a flagship species, is one that people are likely to find attractive and interesting. The flagship species is used to raise public awareness and motivate people to take action to protect the threatened habitat. People’s support of the flagship species results in protection for all the plant and animal species living in the threatened area.
按照原词重现规则，我们找到了这句话：“This species, called a flagship species, is one that people are likely to find attractive and interesting.”从这句话理解，旗舰物种是一种人们觉得有趣又吸引人的物种。可是这并不是短文里所说的重点，通读短文之后，我们不难知道，flagship species的特点是被选为代表，引起人们的注意，去保护一个栖息地，而上面那句话只是说明了旗舰物种的一个通常具备的特征，所以不能作为它的定义。它的定义我们可以前面的一句话“select a particular species to represent the threathened habitat to the general public”，这个应该是比较接近的定义的一句话，但是它只说了被选出来作为代表，而目的没有明确，为什么被选出来则没有提及。我们再看后面的一句话“is used to raise public awareness and motivate people to take action to protect the threatened habitat.”，这里说明了旗舰物种存在的意义。所以定义应该是两句话结合那么我们可以说“flagship species is a particular species selected to represent a threatened habitat to the genneral public to to raise public awareness and motivate people to take action to protect the threatened habitat.”