2026年真题09

Listen to a talk in an economics class. Imagine that you have a full time job, but you want to take a year off to go back to school. What is it going to cost you? Of course there's the cost of tuition for your classes, plus living expenses. But what about the money you're no longer earning at your job because you're now a student? We call that the opportunity cost. Opportunity cost refers to the value of the next best alternative that must be given up when making a choice. It's a fundamental principle in economics that helps individuals and businesses understand the true cost of their decisions. My exercise in imagination illustrates a personal decision, but businesses also face opportunity costs in their operations. For instance, a company may choose to invest in new equipment rather than spend money to expand its product line. The opportunity cost of this decision is the potential revenue that could have been generated from the new products. Understanding opportunity cost helps individuals as well as businesses make informed decisions that maximize their benefits and minimize their losses. It's important to note that opportunity cost is not always measured in financial terms. It can also be related to factors like time, convenience or personal satisfaction. For that reason, opportunity cost can be difficult to quantify, especially when dealing with non monetary factors. Have you ever had to make a decision that included an opportunity cost? Take a few minutes now to think and then I'll ask for volunteers to share.

Listen to a talk in a science class today. I want to tell you about an unusual phenomenon that scientists noticed in the Pacific Ocean in the early 1990's. The scientists were recording sounds using hydrophones positioned on the ocean floor in the North Pacific. Hydrophones are specially designed microphones that allow scientists to collect acoustic data underwater. While most of the undersea noises picked up by the hydrophones emanated from whales, ships engines, or earthquakes, the scientists monitoring the hydrophones detected a number of sounds that they could not identify. One was a regular series of rising infrasonic tones that is a very short wavelengths below those humans can hear. The scientists labeled these very low frequency noises up sweep. At first, these sounds were thought to be the songs of whales migrating in the Pacific. However, scientists who study whale acoustics eventually ruled out this possibility and the origin of the up sweep sounds remained unknown. So what is the source of the rising tones detected by the hydrophones? The sounds were ultimately tracked to an area of inferred volcanic seismic activity, a chain of undersea mountains in the South Pacific. Some scientists believe that if these mountains contain an active volcano, the source for the mysterious up sweep sounds may be hot volcanic lava coming in contact with cold sea water.

Listen to a talk in a biology class. In the early 1900s, sea otters, marine mammals that feed on invertebrates including sea urchins, were nearly wiped out along the United States Pacific Coast by fur hunters. With otters gone, urchin numbers exploded, destroying kelp forests. That kelp is a type of seaweed and it's sea urchins favorite food. This left countless marine species without the protective habitat that kelp forest provided to them. In 1972, hunting sea otters was banned. As otters made a comeback, urchin numbers dropped, kelp forest grew back, and biodiversity flourished. Scientists realized otters were a keystone species, organisms whose impact on ecosystems is far greater than their numbers suggest. A similar case occurred in Yellowstone National Park. Wolves, the parks top predator, had been eradicated. { 1:00 } Populations of elk, a deer like animal and a favorite prey for wolves, soared and their huge populations damaged local vegetation, including the Willow and Aspen trees for which the park had been famous. In the 1990s, wolves were reintroduced to the park to get the elk population under control. But the wolves didn't just cut elk numbers, they changed elk behavior. Afraid of being eaten by wolves, the elk avoided stream side areas where they're especially vulnerable. This helped Willow and Aspen trees re establish themselves there, and the trees brought back Beavers, animals that live in streams and build dams to create ponds for themselves. The Beaver dams created habitats for fish, birds and amphibians, a huge cascading effect because of this other keystone species.

Listen to a talk in an art history class. When we think about paintings, we often focus on their subject, their style, or even the type of paint used. What we often overlook is the material underneath the paint, what we call its support or sometimes the substrate. This is the surface on which the paint is applied. The support is more important than you might think. Before the 14th century, most paintings were created on wooden panels. Wood was strong and durable, but it posed serious challenges. Large panels were extremely heavy, making transport difficult. Because of this, artists were limited in how big their works could be. Typical subjects for panel paintings were small devotional images, altar pieces, and portraits, works intended for private chapels or fixed locations rather than large public spaces. { 0:58 } In the early 14th century, artists in Italy, especially in Venice, began turning to canvas as a support for their paintings, and by the late 15th century its use had spread widely. Canvas was light and flexible, so paintings could be moved easily and made much larger. This portability meant that monumental works could be displayed in civic buildings, palaces, and even transported for festivals. This brought art beyond the confines of churches and into broader public life. This new use of canvas wasn't just a technical change. It transformed art because it enabled ambitious subjects like vast historical scenes and mythological narratives. For example, Paulo Varanes's The Wedding at Cana, which is a massive banquet scene filled with dozens of figures and rich architectural detail.