听力原文： Not until some 200 years ago did the world population begin increasing at a rapid rate. In many parts of the world, people's health began to improve as a result of improved sanitation, the drainage of swamps, and, later, such developments in the field of medicine as the use of antibiotics. Increased trade brought better economic conditions in many countries. All these improvements made it possible for man to live longer. The standard of livings throughout the world began to rise as a result of advances in agriculture and in the processing of agricultural products. These included better farming methods, mechanization, fertilization, and refrigeration. Improved transportation helped to open new territories for settlement in the Western Hemisphere and in Australia. It also helped in distributing the great abundance of agricultural and industrial products that began to be available.
The combination of a high birth rate and a low death rate is creating a rapid population increase in Asia, Africa and Latin America. Experts fear that the population may soon grow faster than the food supply available in these continents, which are so dependent upon agriculture. Conditions of absolute over-population would result in many countries. In 1798 the English economist Thomas R. Malthus (1766-1834) said in his famous Essay on the Principle of Population that population increases at a faster rate than the food supply does. Therefore if such natural checks as war, starvation, and disease did not decrease the population, the world would outgrow its food supply. However, Malthus could not foresee that in many parts of the world, medical, scientific, and technological advances would wipe out these natural checks to population growth.
Solutions to the problem of overpopulation are not easy to find. In many cases a people's culture and way of life stand in the way of such matters as late marriages and birth control, which would help lower the birth rate. A change from an agricultural to an industrial economy would provide another answer. Many countries are planning such a change, but they lack the raw materials, capital, transportation facilities, technical skills, and markets for products. Migration from countries that are seriously overpopulated might help. In many cases, however, the countries to which migrants want to go have laws that prevent many of the migrants from entering.
Questions:
11. Which of the following factors for the improvement of people's health in many parts of the world is not mentioned in the talk？
12. What brings about better economic conditions in many countries？
13. What is the main reason for opening up new territories in the Western Hemisphere？
14. What is Malthus's population theory？
15. By whom are late marriages and birth control favored？
(31)

A. Better education.
Better sanitation.
C. Better medicine.
D. Both B and C.