怎么样使北极熊在夏天里感觉凉爽？
文章最后一段讲述的是北极熊数量减少的原因，由于人类的活动引起气候变暖，因此使北冰洋的冰的面积减少，从而使北极熊的数量变少。
B. The sea ice is melting earlier and forming later. C. The climate is changing due to people's activities. D. People killed too many polar bears.
文章最后一段讲述的是北极熊数量减少的原因，由于人类的活动引起气候变暖，因此使北冰洋的冰的面积减少，从而使北极熊的数量变少。
B. The sea ice is melting earlier and forming later. C. The climate is changing due to people's activities. D. People killed too many polar bears.
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