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下列通商口岸中，哪些是在《天津条约》中被迫开放的？ 中国近现代史纲要 阅读理解：阅读下列短文，回答文后问题，选择最佳答案Trees mainly serve man in three important ways: They provide him with wood and other products; they provide him shade; and they help to prevent droughts and floods.Unfortunately, in many parts of the world, man has not realized that the third of these services is the most important．In his eagerness to make money from trees, he has cut them down in large numbers, only to find that without them he has lost the best friends he had. And besides, he is usually too careless to plant and look after new trees. So the forests slowly disappear.This does not only mean that man will have fewer trees. The results are even more serious: for where there are trees, their roots break up soil allowing the rain to sink in and also bind(固定) the soil, thus preventing it from being washed away easily；but where there are no trees, the rain falls on hard ground and flows away, causing floods and carrying away the rich top-soil. When the top-soil is gone, nothing remains but worthless desert.Two thousand years ago，a rich and powerful country cut down its trees to build warships, with which to gain itself an empire．It set up the empire, but, without its trees, its soil became poor and grew weak. When the empire fell to pieces, the home country found itself faced by floods and starvation(饥荒)．3. Land becomes desert after all trees are cut down because _ _ _ _ _ _ _ _ _ _ . A、 A. roots of trees break up the soil B、 B. no tree keeps the rain and protects the top-soil C、 C. strong winds bring a lot of sand D、 D. there are too many rainfalls to make it 大学英语1 申请经营活动时应当具有冷藏设施设备和运输工具的药品是 药事管理与法规 止参照系S中有一尺子沿x方向放置不动，运动参照系S’沿x轴运动，S、S’的坐标轴平行.在不同参照系测量尺子的长度时必须注意（）。 大学物理 根据学习的内容，学习可分为机械学习和无意学习. 中学数学教学研究 社会意识的相对独立性告诉我们（） 马克思主义哲学基本原理