A、Each country’s industrial development level is different. B、Each country’s availability of food is different. C、Each country’s

The advantages and disadvantages of a large population have long been a subject of discussion among economists. It has been argued that the supply of good land is limited. To feed a large population, inferior land must be cultivated and the good land worked intensively. Thus, each person produces less and this means a lower average income than could be obtained with a smaller population.(16)Other economists have argued that a large population gives more scope for specialization and the development of facilities such as sports, roads and railways, which are not likely to be built unless there is a large population.
     (17)One of the difficulties in carrying out a worldwide birth control program lies in the fact that official attitudes to population growth vary from country to country depending on the level of industrial development and the availability of food and raw materials. In the developing country where a vastly expanded population is pressing hard upon the limits of food, space and natural resources, it will be the first concern of government to place a limit on the birthrate. In a highly industrialized society the problem may be more complex. A decreasing birthrate may lead to unemployment because it results in a declining market for manufactured goods. When the pressure of population on housing declines, prices also decline and the building industry is weakened. Faced with considerations such as these,(18)the government of a developed country may well prefer to see a slowly increasing population, rather than one which is stable or in decline.
Questions 16 to 19 are based on the passage you have just heard
16. According to the passage, what is the advantage of a large population?
17. Which of the following is NOT the reason why the official attitudes to population growth vary from country to country?
18. According to the author, what would be the ideal birthrate for a highly industrialized country?
19. What does the passage mainly talk about?