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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.
What can we learn about the animal species living on the Arctic tundra?
选项 A、They can survive under the environmental stresses caused by global warming.
B、They are moving to southern areas for food and territory.
C、Their living conditions are influenced by global warming.
D、Their living habits lead to global warming.
答案C
解析 根据第四段第一句“’the Arctic tundra is changing dramatically due.to global warming. ”可知，由于全球变暖，北极苔原发生了巨大变化，即生活在北极苔原上动物物种的生活环境受到了全球变暖的影响。故选C。
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