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托福阅读TPO5真题原文 音频包.docx


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智课网 TOEFL 备考资料托福阅读 TPO5 真题原文+ 音频包摘要: 众所周知, TPO 都是历年托福考试真题,所以难度最接近托福考试,因此 TPO 是备考托福阅读的必备材料,本文为大家分享的托福阅读 TPO5 真题原文+音频包是托福阅读 TPO 中的一部分,小编在这里将完整版的内容分享给大家,有兴趣的考生可以下载观看。很多考生都喜欢反复的练习托福阅读这个环节,因为没有机经预测的帮助显得比较孤僻, 所以今天小编为大家准备的资料是托福阅读 TPO5 真题原文+音频包,我们一起来看看吧。 Minerals and Plants Research has shown that certain minerals are required by plants for normal growth and development. The soil is the source of these minerals, which are absorbed by the plant with the water from the soil. Even nitrogen, which isa gas in its elemental state, is normally absorbed from the soil as nitrate ions. Some soils are notoriously deficient in micro nutrients and are therefore unable to support most plant life. So-called serpentine soils, for example, are deficient in calcium, and only plants able to tolerate low levels of this mineral can survive. In modern agriculture, mineral depletion of soils isa major concern, since harvesting crops interrupts the recycling of nutrients back to the soil. Mineral deficiencies can often be detected by specific symptoms such as chlorosis (loss of chlorophyll resulting in yellow or white leaf tissue), necrosis (isolated dead patches), anthocyanin formation (development of deep red pigmentation of leaves or stem), stunted growth, and development of woody tissue in an herbaceous plant. Soils are monly deficient in nitrogen and phosphorus. Nitrogen-deficient plants exhibit many of

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  • 时间2016-07-10