A、By asking for donations. B、By selling public lands. C、By selling government bonds. D、By exploiting natural resources. B短文中提到，以

We know we have to pay for what we get. If we buy food, we have to pay for it. If a doctor treats us, we know there will be a bill to pay. These are private bills. But there are also public bills to be paid. They are paid by the government. In turn we get the needed services.(19-1)We pay for these services through taxes.
    What would happen if everyone stopped paying taxes? The water supply would stop: the streets might not be cleaned: schools would be closed. We would not want to live in such a city.(20)The chief duty of every government is to protect persons and property. More than three-fourths of government expenses are used for this purpose. The next largest amount of public money goes to teach and train our citizens. Billions of dollars each year are spent on schools and libraries. Also, a large amount of public funds is spent on roads.
    Most of the needed funds is raised by taxes. The law orders us to pay taxes. We have no choice in the matter.
     (21). Years ago the government made money by selling public lands. But most of the best public lands have now been sold. There are still some public lands that contain oil, coal and other natural resources. They could be sold, but we want to save them for future years.(19-2)So, we all must pay our share for the services that make our lives comfortable.
Questions 19 to 21 are based on the passage you have just heard.
19. What does the speaker mainly talk about?
20. What is most of the government money used for?
21. How did the government raise money to pay public bills in the past?