听力原文： For many years, T-shirts were short sleeved undershirts only for men and boys. T-shirts used to be of one color—white. And since they were worn under shirts, they were generally not seen. Today things have changed a lot. T-shirts has become colorful and fashionable. It can be seen almost everywhere and on everyone. Women and children wear T-shirts as well as teenagers, university students and men from all walks of life. T-shirts are worn on the playground, on the beach or in town. They can also be worn for work. Because the T-shirts are relatively inexpensive, smart, comfortable and convenient to wear, they have become one of the newest ideas in fashion over the world. Although T-shirts are now available in a wide variety of bright materials and styles, the most popular kind is the traditional cotton T-shirts with a slogan or a picture printed on the front. A T-shirt may bear a single word, a popular phrase, pictures of sportsmen, or an advertisement. As T-shirts are becoming more and more popular, new designs are coming up all the time. When do people usually wear T-shirts?