在拓扑结构上，快速以太网采用（ ）。A．总线型拓扑结构 B．环型拓扑结构 C．星 发布时间：2017-05-22 19:58 │ 来源：www.tikuol.com 题型：单项选择题 问题： 在拓扑结构上，快速以太网采用（ ）。A．总线型拓扑结构B．环型拓扑结构C．星型拓扑结构D．树型拓扑结构
题型：单项选择题 Lichens may grow on the bark of a tree in a steaming tropical rain forest, on the bricks of big city buildings, on rocks in hot springs, on wind-swept mountaintops, and in the driest desserts. In the arctic, they provide the principal food for caribou, and they are one of the few plants that grow in Antarctica. They are pioneers, appearing in barren rocky areas and starting the formation of soil in which mosses, then ferns, and then other plants can take root. Lichens are a partnership of two plants — fungi and algae. The lichen body is made up of a network of fungal strands. In the upper layers of these grow groups of algae. The two organisms live together to the benefit of both, a relationship known as symbiosis. The fungi provide support, absorb water, and shelter the tender algae from direct sunlight. The algae carry on photosynthesis and provide the fungi with food. The algae can live independently and are recognizable as a species that grows alone. The fungi, on the other hand, cannot live apart from their partners. They can be placed in known classes of fungi but are unlike any species that lives independently. So definite are the form, color, and characteristics of these double organisms that for hundreds of years, they were classified as one. More than 15,000 "species" were named. If these organisms are classified as separate species, it is difficult to fit them into the existing system of classification. But if they are classified separately, these species of fungi seem rather strange. Lichens are a splendid example of the difficulties faced by taxonomists in classifying species.The word "barren" underlined in Paragraph 1 most probably means _______ .A．lifelessB．frigidC．hardD．uncovered 查看答案
题型：单项选择题 关于平均利润的形成，正确的说法有 ( )A．是以资本转移为特征的不同部门之间的竞争导致的结果 B．是社会中所有个别利润的平均化C．平均利润形成后商品的销售将不再按价值出售D．全社会平均利润的总额将小于剩余价值的总额 查看答案