题干

如图所示的电路,电源电压保持不变,电阻R1、R2的阻值分别为10Ω和20Ω,只闭合开关S1,将滑片P移到中点,电压表示数为6V,电阻R1的功率为P1,闭合开关S1、S2,将滑片移到最左端,电阻R2的功率为P2,若P1:P2=2:9.则下列说法正确的是(  )

A:电源电压为18V

B:滑动变阻器的最大电阻为20Ω

C:电路的最大功率为12.15W

D:电路的最小功率为2.7W

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C

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    Renaissance is a French word. It means “rebirth”. It's a strange name for a period of history. What was exactly “ reborn” during the Renaissance?

    To answer this question, we need to look back at the time of the Roman Empire. At this time Roman artists, scientists and writers influenced by Greek ideas were the world's most advanced. They had become skilled observers of the natural world around them, and had become experts in studying animals, plants, the human body or the stars and planets. They wrote down their ideas about what they saw, and based their theories about the world on their observations.

    During the fourth and fifth centuries the Roman Empire slowly broke down. Many of the Romans' art and sculptures were destroyed and some manuscripts(原稿)were lost as well. But most importantly, some of the ancient attitudes were lost. A questioning approach to the world was replaced by an unquestioning one.

    Why did this happen? One reason was to do with the influence of the Christian Church. Through the thousand years following the fall of the Roman Empire, the Church controlled many aspects of life including education and learning. The Church ran all the universities and thought that the aim of a university should be to teach old ideas more clearly, not to introduce new ones. The scholars in the universities were expected to study God and heaven from the Bible and ancient books, rather than the world around them.

    Take medicine for example. The main textbook for doctors had been written by a Greek doctor called Galen more than a thousand years earlier. But when Roger Bacon, a thirteenth-century priest(牧师), said that a new approach to medicine was needed --- doctors should do their own original research instead of reading writers from the past such as Galen-the Church put him in prison.

    By the time of the fourteenth century, however, some parts of the Christian Church were becoming less strict about their ideas and there was a new state of mind among artists, doctors and scientist. People wanted to find out more about the world by studying it. This attitude of investigation had been common in classical scholars, and it was ‘reborn' during the Renaissance.