Passage One
Questions 21 to 25 are based on the following passage.
For many years ，T-shirts were simple short-sleeved undershirts 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 the T-shirt has become fashionable. It can be seen everywhere and on everyone. Women and little children wear T-shirts as do teenagers，university students，and men from all walks of life （各行各业）。T-shirts are worn on playground，at the beach or in town. They can also be worn for work. Yet T-shirts remain relatively inexpensive and long wearing，as well as easy to care for. Smart but comfortable and convenient to wear，they have become one of American‘s newest ideas on fashion.
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 picture printed on the front. A T-shirt may bear a picture，a single word，a popular phrase，or an advertisement. As T-shirts are becoming more and more popular，new designs are coming up all the time.

We can learn from the second paragraph that（）.