During the nineteenth century, when little was known about environmentalism and conservation, it was common to hear people in Eu

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问题     During the nineteenth century, when little was known about environmentalism and conservation, it was common to hear people in Europe and America say that the resources of the sea were unlimited. They believed the world and nature would【B1】______ reproduce all the resources they would need. For example, a【B2】______biologist writing in the mid-nineteenth century【B3】______that none of the great sea fisheries were to be【B4】______. Today, though, there is evidence that the resources of the sea are seriously endangered.
    【B5】______, environmentalists have focused their attention on the land and air. Recently, however, they are beginning to discover that the resources of the sea are in as much danger. The list of endangered【B6】______now included herring and crabs as well as the African elephant, Indian tiger, and the American eagle.
    【B7】______, the threats to fish are more【B8】______in some ways than the threats to animals and birds. This is because【B9】______. Hence, a decline in the fish supply could have extensive effects on hunger and population. Fishermen in the North Atlantic alone【B10】______without depleting fish reserves within the next few years. Rapidly declining sea resources in many parts of the world are problems that cannot be ignored any longer.【B11】______
【B5】

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答案Previously

解析 此处位于句首,后面接一个逗号,显然应该是修饰句子的副词。从下面一句Recently,how-ever…来看,本句与however引导的内容相对.后文是本句的转折。由此猜测,本空格应填写与recently相对的表示时间的副词。
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