Question 21 is based on the passage you have just heard.

Passage Two

    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）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 are 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. So, we all must pay our share for the services that make our lives comfortable.

21. How did the government raise money to pay public bills in the past?

解析：B。该题目为细节题。问题是：过去，政府如何筹集资金支付公共费用？出题点在时间对比处和转折处。根据原文“Years ago the government made money by selling public lands. But most of the best public lands have now been sold”，过去政府通过出售公共土地筹集资金，但是现在大部分优质公共土地都已经出售了。选项B）By selling public lands，与原文内容视听一致，再现原文。因此，此题目正确答案为B。