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In addition to the established energy sources such as gas, coal, oil and nuclear, there are a number of other sources that we ought to consider. Two of these are hydroelectric and tidal power.These two sources are 1 in that they are both renewable. 2 , hydropower is more widely used than tidal. In 3 , a substantial amount of electricity is already produced in HEP (hydroelectric power)stations worldwide, 4 tidal stations are still in the very early 5 of development.As far as geographical 6 is concerned, HEP projects are to be found on lakes and rivers. while tidal 7 are constructed only at river mouths where tidal 8 is great. Unfortunately these are 9 in number. At present HEP stations are found mainly in Norway, Canada, Sweden and Brazil, whereas tidal plants are in 10 in France, Russia and China.As regards capital 11 , both require very high investment. On the other hand, generating 12 are quite low in both cases. In fact, a large scale HEP plant is capable of producing power more 13 than conventional sources, such as coal, oil and nuclear plants. Tidal power also compares 14 with nuclear and oil generated electricity, 15 the amount of money on production. 16 HEP stations, tidal constructions have a long life 17 . It is estimated that they can operate for over 100 years. With respect to 18 of supply, tidal stations 19 from HEP ones in that they often can only supply power 20 . HEP stations, however, provide a constant supply of electricity.
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For centuries the most valuable of African resources for Europeans were the slaves, but these could be obtained at coastal ports, without any need for going deep inland. Slavery had been an established institution in Africa. Prisoners of war had been enslaved, as were also debtors and individuals guilty of serious crimes. But these slaves usually were treated as part of the family. They had clearly defined rights, and their slave status was not necessarily inherited. Therefore it is commonly argued that Africa"s traditional slavery wasmildcompared to the trans-Atlantic slave trade organized by the Europeans. This argument, however, can be carried too far. In the most recent study of this subject, some scholars warned against the illusion that "cruel and dehumanizing enslavement was a monopoly of the West. Slavery in its extreme forms, including the taking of life, was common to both Africa and the West. The fact that African slavery had different origins and consequences should not lead us to deny what it was—the exploitation and control of human beings." Neither can it be denied that the wholesale shipment of Africans to the slave plantations of the Americas was made possible by the participation of African chiefs who rounded up their fellow Africans and sold them as a handsome profit to European ship captains waiting along the coasts.Granting all this, the fact remains that the trans-Atlantic slave trade conducted by the Europeans was entirely different in quantity and quality from the traditional type of slavery that had existed within Africa. From the beginning the European variety was primarily an economic institution rather than social, as it had been in Africa. Western slave traders and slave owners were acted on by purely economic considerations, and were quite ready to work their slaves to death if it was more profitable to do so than to treat them more mercifully. This inhumanity was reinforced by racism when the Europeans became involved in the African slave trade on a large scale. Perhaps as a subconscious rationalization they gradually came to look down on Negroes as inherently inferior, and therefore destined to serve their white masters. Rationalization also may have been involved in the Europeans" use of religion to justify the traffic in human beings. It was argued, for instance, that enslavement assured the conversion of the African evil-believing religions to the true faith as well as to civilization. The relation between the two paragraphs is that in the 2nd paragraph the author
具有清虚热、退骨蒸功效的方剂是
患者阴肿、阴痒、筋痿、阴汗，小便淋浊，舌红苔黄腻。治宜
银花、连翘在清营汤中的作用是
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