About three hundred years ago, there were approximately half a billion people in the world. In the two centuries that followed the population doubled, and, by 1850, there were more than a billion people in the world. It took only 75 years for the figure to double once more, so that now the population figure stands at approximately six and one half billion.
In former centuries the population grew slowly. 46. Famines, wars, and epidemics, such as the plague and cholera, killed many people. Today, although the birth rate has not changed significantly, the death rate has been lowered considerably by various kinds of progress.
Machinery has made it possible to produce more and more food in vast areas, such as the plains of America and Russia. Crops have increased almost everywhere and people are growing more and more food. 47. New forms of food preservation have also been developed so that food need not be eaten as soon as it has grown. Meat, fish, fruit and vegetables can be dried, tinned or frozen then stored for later use.
Improvement in communications and transportation has made it possible to send more food from the place where it is produced to other places where it is needed. This has helped reduced the number of famines.
Progress in medicine and hygiene has made it possible for people to live longer. People in Europe and North America live, on the average, twice as long as they did a hundred years ago. In other countries, too, people generally live much longer than they once did. 48. Babies, especially, have a far better chance of growing up because of increased protection against infant disease. However, all countries do not benefit to the same degree from this program in medicine and hygiene.
In Europe and North America, the growing population has had the advantage of greater quantities of natural resources and food. However, in some places, such as the monsoon countries of Asia, the birth rate has always been very high.
Half the world's people live in Asia, but most of them are concentrated in the coastal regions and on the islands. 49. The same type of populace concentration is true of other continents, although they are often far less populated. There are still vast regions of the larger continents. mountainous areas, deserts, the far north, and tropical jungles.
In prehistoric time, people from Africa and Asia migrated to other continents. 50. Europe was occupied by people from the east, America by groups from Asia. In the nineteenth century, the population of Europe increased rapidly, and living conditions were sometimes difficult because of wars, famines, or political conditions. Many Europeans left their countries to find better conditions to America, Africa and Australia.
During the nineteenth and twentieth centuries, migrations have taken place within certain countries: the cities with their industries have attracted people away from the country. 51. The possibility of earning a fixed salary in a factory or office was more attractive than the possibility of staying on the farm and having one's work destroyed by frost, storms, or droughts. Furthermore, the development of agricultural machinery made it possible for fewer people to do the same amount of work.
Thus, at the same time that the industrial revolution made it possible to produce goods more cheaply and more quickly in factories, and agricultural revolution also took place.
The possibility of earning a fixed salary in a factory or office was more attractive than the possibility of staying on the farm and having one's work destroyed by frost, storms, or droughts. Furthermore, the development of agricultural machinery made it possible for fewer people to do the same amount of work.
【正确答案】：在工厂或办公室里挣到固定工资的可能性，比留在农场让自己的工作被霜冻、暴风雨或干旱毁掉的可能性更有吸引力。此外，农业机械的发展使由更少的人完成同等数量的工作成为可能。
