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 32 to 36. 

      In the United States and other developed countries, air-conditioning is so common that it is difficult to remember what life was like before it existed. First invented in 1902 in Buffalo, New York, air-conditioning keeps homes, cars, offices, and shopping centers cool and dry, all at the push of a button. While many may consider air-conditioning one of life's necessary luxuries, few are aware of how air-conditioning has changed many aspects of the way we now live. One of the first areas where (air-conditioning had an impact was in industry. In the early 1900s factory owners began to use lair-conditioning to create better conditions for the storage of supplies. Before long, however, they realized that air-conditioning was also useful on the factory floor, as it resulted in higher production levels. Air-conditioning has undoubtedly been an important factor in the growth of industry, since it allows manufacturing to continue at the same pace year round even in the warmest climates. 

      Air-conditioning next became common in movie theaters, offices, and stores. Then, after the end of the Second World War, smaller, less expensive air-conditioning units became available, and this made air conditioning affordable for private homes. Many of the returning soldiers and their new families moved to the suburbs outside America's major cities with a desire to put the war behind them and live the good life. Air-conditioned homes were part of that life, and this led to a number of important changes in American society. One big change was in architecture. Formerly, homes were built with high ceilings and second stories so that hot air could rise away from main living areas in the summer. With air-conditioning, inexpensive one-level homes could be kept cool in the hottest weather. Additionally, many homes once had front porches where American families gathered in the evening to escape the heat. Family members could talk to each other and to neighbors or passers-by. With air-conditioning, however, porches disappeared from new houses and people moved indoors instead. Along with other factors, such as the invention of television, this led to a weakening of Americans' sense of community.

In developed countries, air-conditioning is _____.