Zheng He was one of China's most famous explorers. Towards the end of the fourteenth century, his fleet (舰队) sailed to countries far away.

Zheng He had over 300 ships, some of which were over 150 meters long, and could carry up to 1 ,000 people. Besides, the ships carried gold, silver, silk, china and other treasures to give as gifts to the rulers of other countries. Some ships even had earth on board so that the sailors could grow their crops for food.

On Zheng He's first voyage(航海), he set sail across the Indian Ocean. His fleet travelled many days far away from land. One day, they were hit by a storm. All the sailors thought the fleet was going to sink. Then a strange light appeared and after that,the storm passed. The strange light was probably electricity from the thunderstorm (雷雨),but the sailors in Zheng He's fleet believed it was a sign of protection from the gods. With the belief, they were happy to follow Zheng He wherever he led them.

Zheng He completed seven famous voyages between 1405 and 1433. He visited many countries in Asia and Africa. He brought back many gifts from the countries he visited, such as medicines, pearls (珍珠) and strange animals. The most famous of them were a giraffe and a zebra.

In 28 years of travelling, Zheng He had managed to share the glory of China with many different countries. When he died in 1435,the stories of his travels made him one of China's most famous sailors.

Levi Strauss did not invent jeans, but he is considered the first person to make and sell great numbers of them. He was born in Bavaria, an area that is part of Germany. In 1847 he and his family moved to the United States.

Levi Strauss opened a small dry goods store, first in New York, then in San Francisco, California. Among the products he sold were jeans. These pants were especially useful for miners in California. They needed clothing made from a strong material. Jeans are usually made from a heavy cotton cloth called denim.

Levi Strauss partnered with a clothing maker named Jacob Davis. Davis had invented a process for making rivets (铆钉) for jeans. These little metal connectors helped hold the pieces of cloth together to make the jeans stronger.

In 1875, the government gave Strauss and Davis a patent (专利) for their invention. That meant no one else could legally copy it without their permission. In 1928 the Levi Strauss company registered (注册) the word “Levi’s” as a trademark for their product.

The Smithsonian’s National Museum of American History in Washington has one of the oldest known pairs of Levi’s. Writer James Sullivan published a book called “Jeans: A Cultural History of an American Icon.” In the book, he says jeans show two American values, creativity and rebellion.

Cowboys wore jeans in the old Wild West. In the 1950s, people saw famous Hollywood actors like James Dean and Marlon Brando wearing jeans in movies.

Today jeans come in blue but also lots of other colors and in many styles and at all prices.

Over the course of more than 250 years, the US Postal Service has gone through many changes, including switching its focus from newspapers to package delivery service.

In the early 1830s, the Postal Service focused on delivering newspapers to keep Americans informed and connected. To keep newspaper subscriptions cheap and accessible, the Postal Service charged high prices for letter postage as much as a full-day’s wages. In order to help the expansion of the passenger transportation network in the new nation, the agency often shared the letter delivery with stagecoach lines. Later, it did the same for private steamboats and railroads, even airlines

But the competition for the letter delivery became so fierce that a wave of laws between 1845 and 1851 made the Postal Service the only letter-carrier and set aside an annual budget to support the agency. Helped by lowered rates, letters soon became the agency’s main business.

In 1863, the Postal Service began to experiment with home delivery, instead of just carrying letters from post office to post office. By the dawn of the 20th century, even remote farmers’ letters were dropped into their mailboxes. Since then, home delivery has become a “universal public service (UPS)” that every American deserves to receive at a low price.

By the early 20th century, the Postal Service had set a four-pound limit on mail: Anything heavier was supposed to be left to private companies. But the four largest private carriers secretly cooperated to charge confusing and often terribly high rates. In 1913, the Postal Service eventually took the parcel (包裹) service away from the private carriers.

Now the Postal Service’s only growing business is package delivery fed by the online shopping addictions. Since it is required by law to visit every household six days a week, the Postal Service now offers cheap rates to private companies like Amazon and FedEx to deliver their goods to our doorsteps. However, most Americans think that it is unfair to use taxpayer’s money to help such big private companies to deliver their goods.