International trade develops because certain countries are able to produce some goods more efficiently than other countries. They exchange goods to satisfy their needs and wants. Efficient production may be the result of several factors. A certain climate in a particular country may allow that country to grow agricultural products in large quantities. For instance, the climates in the United States and Canada are suitable for production of large amounts of wheat. Natural resources such as oil or coal are rich in other countries. Countries with a large pool of unskilled laborers are able to produce products which are labor intensive more cheaply than countries with highly paid, skilled labor forces. Another factor is geographical location.
The Scottish economist, Adam Smith, believed that in a free market countries produce whatever they can most efficiently grow or manufacture. In other words, if they can make more money growing cotton than making cloth, they grow
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[单项选择] Adaptation of Living Things
Certain animals and plants develop characteristics that help them cope with their environment better than others of their kind. This natural biological process is called adaptation. Among the superior characteristics developed through adaptation are those that may help in getting food or shelter, in providing protection, and in producing and protecting the young. That results in the evolution of more and more organisms that are better fitted to their environments.
Each living thing is adapted to its way of life in a general way, but each is adapted especially to its own distinct class. A plant, for example, depends upon its roots to fix itself firmly and to absorb water and inorganic chemicals. It depends upon its green leaves for using the sun’’s energy to make food from inorganic chemicals. These are general adaptations, common to most plants. In addition, there are special adaptations that only certain kinds of plant
A. A living thing may have the ability to create an environment of its own B. A living creature may have the ability to remain still when an enemy is near. C. A living creature may have the ability to make food from its inorganic chemicals D. A living creature may have the ability to change the color of its skin. [单项选择]
All friendships require a certain amount of chemistry. But when two people of the opposite sex become friends, sometimes those friendly feelings can start to resemble something more like sexual tension. [单项选择]
Normally a student should attend a certain number of classes to graduate, and each lesson which he attends offers him a credit (学分) which he may count towards a degree. In a lot of American universities the total work for a degree consists of six courses each lasting for one term. A typical course consists of four classes per week; normally a student would expect to take four years attending two terms each year. It is possible to spread the period of work for the degree over a longer period. It is also possible for a student to move between one university and another during his degree course, though this is not in fact done as a regular practice. [单项选择]Cells cannot remain alive outside certain limits of temperature, and much narrower limits mark the boundaries of effective functioning. Enzyme systems of mammals and birds are most efficient only within a narrow (31) around 37℃; a (32) , of a few degrees from this value seriously impairs their functioning. Even though cells can survive wider (33) , the integrated actions of bodily systems are impaired. Other animals have a wider tolerance (34) changes of bodily temperature.
For centuries (35) has been recognized that mammals and birds differ from other animals in the way they regulate body temperature. Ways of (36) the difference have become more accurate and meaningful over time, but popular terminology still reflects the old division (37) " warm blooded" and "cold blood- ed " species; warm blooded included mammals and birds, (38) all other creatures were considered cold blooded. (39) more species wer A. bottoms B. lengths C. depths D. darkness 我来回答: 提交
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