听力原文： The world's population continues to grow. There now are about 4 billion of us on earth. The number could roach 6 billion by the end of the century and 11 billion in another 75 years. Experts have long been concerned about such a growth. Where will we find the food, water, jobs, houses, schools and health care for all these people？ A major new study shows that the situation may be changing. A large and rapid drop in the World's birth rate has taken place during the past 10 years. Families generally are smaller now than they were a few years ago. It is happening in both developing and industrial nations. Researchers said they found a number of reasons for this. More men and women are waiting longer to get married and are using, birth control devices and methods to prevent or delay pregnancy. More women are going to school or working at jobs away from home instead of having children. And more governments, especially in developing nations, now support family planning programs to reduce population growth. China is one of the nations that has made great progress in reducing its population growth.
China has already cut its rate of population growth by about one half since 1970. Each Chinese family is now urged to have no more than one child. The hope is to reach a zero population growth with the total number of births equaling the total number of deaths, by the year
(33)

An economic policy of a country.
B. An economic policy of a family.
C. TV programs designed for a family.
D. A birth control policy of a country.