Questions 47 to 51 are based on the following passage. According to the Encyclopedia of Stress, "stress" is one of the most frequently used but ill-defined words in the English language. We say we’re stressed when we’re late for work and when we can’t pay our bills. We laugh about the stress of the holidays and cry over the stress of a divorce. Even an ostensibly (表面上) happy occasion — such as the birth of a child — can be stressful. The encyclopedia defines stress as a "real or interpreted threat to the physiological and psychological integrity of an individual that results in physiological and/or behavioral responses". In other words, stress is any change in your world that evokes some reaction from you. If you’re a neatness nut, having 10 people staying in your house for a long weekend could be incredibly stressful; but if you don’t mind chaos and clutter, then let the fun begin. If you thrive on to-do lists and deadlines, a week with absolutely nothing to do and nowhere to go could make you crazy; another person might feel positively reborn. "People talk about stress as though it’s a bad thing," says stress researcher Catherine M-Stoney, Ph.D., a psychology professor at Ohio State University, "but stress exists inside us. It’s really the interaction between what’s in our environment and how we cope and deal with it." Stress is often linked to a short-lived event, such as an argument. But it can be prolonged as well in fact, the persistent yet subtle pressures of modern-day living are an ever-increasing — yet harder to diagnose — cause of stress. Doctors identify three main classes of stress: Acute stress. This is the most common form, stemming from the demands and pressures of the recent past and the anticipated demands and pressures of the near future, such as a fast-approaching deadline. Episodic acute stress. People in this category move from one episode of acute stress to another. Typically they live lives filled with chaos and crisis. They take on too much, they’re always running late, and their homes are filled with clutter. They never seem to slow down, are quick to anger and, not coincidentally, have higher rates of heart disease. Chronic stress. This is the subtler, prolonged stress — often linked to large life issues — that wears you down every day. It exists in the background of your daily routine. You become so used to it, you don’t even know it’s there anymore. In the modern society, an ever-increasing cause of stress is pressures of living that ______ affect people