（3）Vitamins
It was not until the beginning of this century that it was recognized /that certain substances were essential in the diet to prevent or cure some diseases. / These substances are now known as vitamins. / They are vital for growth, good health,/ and maintenance of the normal functions of the body. / A well-balanced diet should provide all the vitamins we normally require. / Those of us who are fortunate enough to be able to buy sufficient food/ should not suffer from vitamin deficiency. / However, for various reasons,/ some people do not maintain a balanced diet. / People often lose their appetite because of illness. / People living alone may not bother to eat proper meals,/ and people on a diet may not eat sufficient quantities of necessary foods. / Moreover, modern methods of preserving, freezing and long-time storage of food,/ together with over cooking, can destroy many of the vitamins. / (145 words)
(4)Salt
We do not know when man first began to use salt, / but we do know that it has been used in many different ways throughout history. /Historical evidence shows, for example, that people who lived over 3000 years ago ate salted fish. / Thousands of years ago in Egypt, salt was used to preserve the dead. /
Stealing salt was considered a major crime during some periods of history. / In 18th century, for instance,/ if a person was caught stealing salt, he can be put in jail. /History records that about ten thousand people were put in jail during that century for stealing salt! / About 150 years before, in the year 1553, / taking more salt that one was allowed to was punishable as a crime. /The offender’s ear was cut off. /
Salt was an important item on the table of royalty. /It was traditionally placed in front of the king when he sat down to eat. /Important guests at the king’s table were seated near the salt. /Less important guests were given seats farther away from it./ (175 words)
（5）The first trans-continental railroad
When the first trans-continental railroad was completed in 1869, native lands seemed even more desirable, and movement westward increased as industrialism spread. The railroads spurred America’s transformation from an agricultural economy, or one based primarily on farming, to an economy where capitalism, or private ownership of businesses, prevailed. Industry in America developed far more rapidly than it had in Europe. Factories and mills spread quickly throughout New England prior to the Civil War due to good supplies of natural resources such as iron and coal, and the ease of transporting finished goods along the many navigable rivers. This in turn lead to the building of more railroads and canals to handle the increased traffic.
(6)Mississippi river
Mississippi river is the largest and most important river in North America. It has played a central role in the exploration and economic development of the continent. Many cities and towns began along the Mississippi and continue to depend on the river for their economic base, because the river makes it possible for large vessels to use the river. About 282 million metric tons of freight is carried on the river each year. The most important cargoes on the river are items such as coal, petroleum products, sand, and grain. The Mississippi Valley has rich soils, formed by thousands of years of deposition by the river. It supports agriculture, especially feed grains and soybeans in the north and cotton and rice in the south. The upper valley once contained vast nutritious beds, which were the basis of an extensive fishery in the 19th and early 20th centuries, but these were severely exhausted and are no longer commercially significant.
（7）The Bald Eagle
The bald eagle is a bird of mixed fortunes. Having been declared the national symbol of the USA should have guaranteed it a good chance at life, with protection from hunters. Far from this being the case, the bird was, until recently, actively hunted as a pest, and many individuals have fallen to the bullet over the years. Currently, it enjoys an element of protection and its numbers are beginning to recover. The American Bald Eagle is a fairly large eagle which, in captivity, with access to medical care, regular food and, of course, no threat from predators or humans may enjoy a life expectancy in excess of 40 years. In the wild, their life span will depend on such things as food, climate, persecution by hunters, farmers, illness and a host of other factors.
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