Dogs were first domesticated from wolves at least 17,000 years ago, but perhaps as early as 150,000 years ago based upon recent

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问题     Dogs were first domesticated from wolves at least 17,000 years ago, but perhaps as early as 150,000 years ago based upon recent genetic fossil and DNA【B1】______ . In this time, the dog has developed into hundreds of breeds with a great degree of【B2】______ . For example, heights at the shoulder range from just a few inches to roughly three feet, and colors range from white to black, with reds, grays, and browns【B3】______ in tremendous【B4】______ .
    Dogs are highly social animals and this【B5】______ in their overall behavioral system【B6】______ for their trainability, playfulness, and ability to fit into human【B7】______ and social situations. This has earned dogs a【B8】______ position in the realm of interspecies relationships.【B9】_____________________ are thought to be reflections of the human idea of love and friendship, leading many dog owners to view their pets as full fledged family members. Dogs seem to view their human companions as members of their pack, and make few, if any, distinctions between their owners and fellow canines.【B10】__________________________ . For dogs that do not have traditional jobs, a wide range of dog sports provide the opportunity to exhibit their natural dog skills. In many countries, the most common and perhaps most important role of dogs is as companions. Dogs have lived with and worked with humans in so many roles that【B11】____________________________ .
【B10】

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答案Dogs play a variety of roles in society and are often trained as working dogs

解析 本句较简单。variety 和37题的variation 是同根词。
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