Hi, guys. I want to talk about how to solve the question #1 of TOEFL listening, i.e., the main idea question. These are the two clues:
The main idea can usually be found in the first segment (or paragraph if you take notes the way I explained) of the lecture. The professor will say it explicitly or implicitly. Of course there are exceptions, and the main idea might not start until after the second paragraph. This is usually the case when the professor has to set the stage (has to explain various concepts) before she can talk about the main topic of concern.
The correct choice is normally phrased using a general term
I am going to discuss two hard questions today. The first one is hard since the clue phrase is implicit. The second question is hard since the main point appears much later in the lecture.
Example 1. Bryce Canyon (hard) TPO 63
Lecture content:
The professor begins the lecture with a field trip to Bryce Canyon National Park, adding this phrase, “remarkable geologic phenomena.” So we can infer that the lecture is about some remarkable geologic phenomena. His lecture culminates with the explanation of how hoodoos were created. So we can infer this:
remarkable geologic phenomena = hoodoos, slot canyons, windows
To explain the hoodoo formation, he discusses the effects of weathering and erosion on the sedimentary rocks of the Canyon. So, the main idea is how weathering and erosion created the remarkable shapes of the rocks.
Q: What is the lecture mainly about?
A . The length of time required to produce sedimentary rocks
B . The role of climate conditions in the creation of sedimentary rocks
C . Some processes that produced a specific group of rock formations
D . Some unique geologic features found in canyons in the United States
Analysis
A: The professor briefly talks about the creation of the sedimentary rocks of the Bryce Canyon (in the second para). But he says this is “obvious.” But we are looking for something “remarkable.” So A is out.
B: The professor talks about the climate conditions, freezing winter and dry summer, to explain how the sedimentary rocks came to change their shapes, not to explain the creation of sedimentary rocks. So B is out.
C: The professor explains the creation of the remarkable geologic phenomena in light of the weathering and erosion on the sedimentary rocks of the Bryce Canyon. “Weathering and erosion” are instances of processes (general term). So C is a good choice.
D is factually incorrect. The professor talks about one US canyon, the Bryce Canyon, and one Australian Canyon. So D is out.
Example 2: Sociology (hard) TPO 61
Lecture content:
The professor goes on and on explaining why sociology is an interdisciplinary study by way of explaining how it borrows ideas from psychology, biology, and cognitive science. She also talks about sympathy groups and social groups. Then she finally arrives at a point where she can introduce the main topic of the lecture: the Dunbar hypothesis. To talk about this, she asks, “Why are there just a dozen people in a sympathy group?” She offers an explanation: a group size is a function of the size of the neocortex in the brain, which is called the Dunar hypothesis. According to the hypothesis, the expected maximum social group size for the human species is 150. She then goes on to talk about how to confirm the Dunbar hypothesis in mammals. So the main topic of the lecture is about the Dunbar hypothesis.
Q: What is the lecture mainly about?
A . The role that the neocortex plays in human memory
B . The connection between neocortex size and social relationships in mammals
C . Various studies that compare social group sizes in humans and other mammals
D . Ways that humans can expand the size of their social groups
Analysis
A is wrong since the topic is not the role that the neocortex plays in human memory, but the role that the neocortex plays in a group size
B is about the Dunbar hypothesis. social relationships = sympathy groups and social groups
C Studies were made not to compare social group sizes in humans and other mammals, but to test the Dunbar hypothesis. That is, animals with a larger neocortex also have a bigger social group.
D is not the point at all.