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 questions from 30 to 34 

     During the early years of this century, wheat was seen as the very lifeblood of Western Canada. When the crops were good, the economy was good; when the crops failed, there was depression. People on city streets watched the yields and the price of wheat with almost as much feeling as if they were growers. The marketing of wheat became an increasingly favorite topic of conversation. 

     War set the stage for the most dramatic events in marketing the western crop. For years, farmers mistrusted speculative grain selling as carried on through the Winnipeg Grain Exchange. Wheat prices were generally low in the autumn, but farmers could not wait for markets to improve. It had happened too often that they sold their wheat soon after harvest when' farm debts were coming due, only to see prices rising and speculators getting rich. On various occasions, producer groups asked for firmer controls. but governments had no wish to become involved, at least not until wartime wheat prices threatened to run wild. 

     Anxious to check inflation and rising living costs, the federal government appointed a board of grain supervisors to handle deliveries from the crops of 1917 and 1918. Grain Exchange trading was suspended, and farmers sold at prices fixed by the board. To handle the crop of 919, the government appointed the first Canadian Wheat Board, with full authority to buy, sell, and set prices. 

What is the main purpose of the passage?