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  3. Tundra ecosystems are treeless regions found in the Arctic and on the tops of mountains, where the climate is cold and windy and

Tundra ecosystems are treeless regions found in the Arctic and on the tops of mountains, where the climate is cold and windy and

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问题     Tundra ecosystems are treeless regions found in the Arctic and on the tops of mountains, where the climate is cold and windy and rainfall is low. Tundra lands are snow-covered for most of the year, until summer brings a burst of wild flowers.
    The Arctic tundra, where the average temperature is rather low, supports a variety of animal species, including Arctic foxes, polar bears, Arctic wolves, caribou, snow geese and musk oxen. The summer growing season is just 50 to 60 days, when the sun shines 24 hours a day.
    The few plants and animals that live in the harsh conditions of the tundra are essentially clinging to life. They are highly vulnerable to environmental stresses like reduced snow cover and warmer temperatures brought on by global warming.
    The Arctic tundra is changing dramatically due to global warming. Already, more southern animals like the red fox have moved onto the tundra. The red fox is now competing with the Arctic fox for food and territory.
    Another major concern is that the melting of the permafrost (永冻土层) is contributing to global warming. Estimates suggest that about 14 percent of the Earth’s carbon is tied up in the permafrost. Until recently, the tundra acted as a carbon sink and captured huge amounts of carbon dioxide from the atmosphere as part of photosynthesis(光合作用). This process helped keep the amount of this greenhouse gas from accumulating in the atmosphere. Today, however, as the permafrost melts and dead plant material rots(腐烂) and releases CO2, the tundra has changed from a carbon sink to a carbon contributor.
As for the current situation of the Arctic tundra, which of the following is NOT among the consequences caused by global warming?
选项 A、The burst of wild flowers.
B、Reduced snow cover.
C、Warmer temperatures.
D、The movement of the red fox.
答案A
解析 根据第一段最后一句“…until summer brings a burst of wild flowers. ”可知，在夏天苔原上会长出许多野花，所以A项不是全球变暖的结果。根据第三段最后一句“They are highly vulnerable to environmental stresses like reduced snow cover and warmer temperatures brought on by global warming. ”和第四段第一、二句“The Arctic tundra is changing dramatically due to global warming. Already, more southern animals like the red fox have moved onto the tundra. ”可知，由于全球变暖+积雪覆盏减少，气温上升，赤狐也迁到了苔原上，所以B、C、D三项是全球变暖的结果。故选A。
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