B. the invention of the printing press.

　　C. the European discovery of America.

　　D. a reawakening of science and the Protestant Reformation.

　　31. What is the major characteristic of the new society today ?

　　A. Labor will be the basis of wealth.

　　B. Class conflict will appear.

　　C. Knowledge will be used as an economic resource.

　　D. People who provide various types of services must be socially and economically disadvantaged.

　　D

　　A green roof is a roof of a building that is covered with vegetation over a waterproof membrane (防水膜). It is a proper method of growing plants on the roof and does not refer to the mere green color of the roof. People benefit a lot from these green roofing systems, and they are gaining popularity day by day.

　　Human beings have occupied major areas of land and transformed them into huge buildings, which has severely affected the environment and the natural habitat of bird and insects. Green roofing compensates for that. It creates a natural habitat for creatures like bees, grasshoppers and other insects.

　　Modern roofs need a lot of energy to control the temperatures in winter and summer. However, green roofs reduce the amount of energy required for controlling temperatures, thus making them energy-efficient. As green roofing is highly energy-efficient, it can act as a encouragement for people who are interested in green roofing systems and their benefits. It will increase the market value of the building and fetch the owner a great share of profit.

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