What is the main point the author makes in the passage

Câu hỏi :

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions. 

     At the turn of the twentieth century, people's attitudes toward money were far more conservative than they are today. Borrowing and being in debt were viewed as a moral failing, almost as a disgrace. Thrift and saving were highly prized, and people who needed to borrow to make ends meet were seen as careless, unreliable, or extravagant. The focus in the economy as a whole was on developing large corporations like railroads, oil companies, and other companies that produced basic goods and services. 

     Then, in the 1920s, the economy changed. A huge network of banks and financial institutions developed, helping money to move more quickly and easily through the economy. At the same time, the economy was increasing its focus on consumer goods-clothing, cars, household appliances, and other things that individuals buy. To help promote the sale of these items, consumers were encouraged to buy on credit. If they could not afford an item right away, a store or a bank might lend them the money, which they could pay back in installments. 

     With the development of consumer credit and installment purchases, people's attitudes toward debt and spending changed. The model citizen was no longer someone who was thrifty, buying only what he or she needed. People were respected less for being thrifty than for knowing how to use their money to buy as many things as possible - an attitude that persists at the turn of the twenty-first century. 

What is the main point the author makes in the passage?