题目内容
听力原文： When men first lived on the earth a long time ago, they had no proper place to live in. In order to get away from the heat of the sun, to keep themselves warm and dry, they found caves. Caves really gave them some kind of help. Some of these early men built their shelters up in the tree to escape wild animals. They had a hard life and had to go about from place to place for food. Much later on, their lives began to change. They learnt how to keep animals in herds. As they had to move their herds of animals from place to place for grassland, they had to build shelters which were easily carried about.
When they finally learnt the art of farming, they had to clean forests and started planting crops. After that, they had to think about building more permanent shelters. Old houses were built at first with wood and they even use grass as roofs. This went on for a long time. They kept making their houses better. Today, houses of all kinds are built. They are strong, permanent and can last a very long time.
(30)
查看答案
搜索结果不匹配？点我反馈
更多问题
给定关系模式R(U，F)，U＝{A，B，C，D，E，F}，F＝{B→F，D→A，A→E， AE→B}，那么属性A的闭包为(62)，R的候选关键字为(63)。
A．The terrible noise in the library.B．The heat inside the library.C．The small room in
A．Prof. Brown has got into trouble.B．The woman regrets taking up much of Prof. Brown's
NASA and the Associated Landscape Contractors of America(ALCA) have【B5】the findings of a 2-year study that【B6】the common indoor plant may provide a natural way of helping【B7】"Sick Building Syndrome."
Research【B8】the use of biological processes as a means of solving environmental problems, both on the【B9】and in space habitats(栖息地), has been【B10】out for many years by Dr. Bill Wolverton,【B11】a senior research scientist at NASA's John C. Stennis Space Center, Bay St. Louis, Miss.
Based on preliminary evaluations of the use of common indoor plants for indoor air purification and revitalization(恢复活力), ALCA【B12】NASA to fund a study using about a dozen popular varieties of ornamental plants to determine their【B13】in removing several key pollutants associated with indoor air pollution. NASA research on indoor plants has found that living plants are so【B14】at absorbing contaminants in the air that some will be launched into【B15】as part of the biological life support system aboard future orbiting space stations. 【B16】more research is needed, Wolverton says the study has shown that common indoor landscaping plants can remove【B17】pollutants from the indoor environment. "We feel that future results will provide an even【B18】argument that common indoor landscaping plants can be a very effective part of a system used to provide pollution【B19】homes and work places," he【B20】.
【B1】
微信支付 
支付宝支付