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  3. Plants in Desert Only special plants can survive the terrible climate of a desert, for these are regions where the annual ra

Plants in Desert Only special plants can survive the terrible climate of a desert, for these are regions where the annual ra

admin2014-05-13  30
问题                             Plants in Desert
    Only special plants can survive the terrible climate of a desert, for these are regions where the annual range of the soil temperature can be over 75 °C . Furthermore, during the summer there are few clouds in the sky to protect plants from the sun’ s ray. Another problem is the fact that there are frequently strong winds that drive small, sharp particles of sand into the plants, tearing and damaging them. The most difficult problem for all forms of plant life, however, is the fact that the entire annual rainfall occurs during a few days or weeks in spring.
    Grasses and flowers in desert survive from one year to the next by existing through the long, hot, dry season in the form of seeds. These seeds remain inactive unless the right amount of rain falls. If no rain falls, or if insufficient rain falls, they wait until the next year, or even still the next. Another factor that helps these plants to survive is the fact that their life cycles are short. By the time the water from the spring rains disappears—just a few weeks after it falls—such plants no longer need any.
    The perennials(多年生植物)have special features that enable them to survive as plants for several years. Thus, nearly all desert perennials have extensive root systems below ground and a small shoot system above ground. The large root network enables the plant to absorb as much water as possible in short time. The small shoot system, on the other hand, considerably limits water loss by evaporation(蒸发).
    Another feature of many perennials is that after the rainy season they lose their leaves in preparation for the long, dry season, just as trees in wetter climates lose theirs in preparation for the winter. This reduces their water loss by evaporation during the dry season. Then, in next rainy season, they come fully alive once more, and grow new branches, leaves and flowers, just as the grasses and flowers in desert do.
The shoot system of perennials can help the plants absorb less of the sun’ s ray.
选项 A、Right
B、Wrong
C、Not mentioned
答案B
解析 利用题干中的“The shoot system”作为线索词，可以把第三段最后一句确定为答案相关句。这句话表明，茎轴系统极大地限制了蒸发所带来的水分损失，而不是说茎轴系统能减少植物对太阳光线的吸收。可见题干与原文的说法不符。
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