世界上第一条地铁在1863年建于( )。
A．纽约
B．巴黎
C．阿姆斯特丹
D．伦敦
参考答案：D
解析： 世界上首条地下铁路系统是在1863年开通的伦敦大都会铁路，是为了解决当时伦敦的交通堵塞问题而建。1898年10月4日，巴黎地铁开始动工兴建，1900年7月19日，巴黎地铁首条路线随巴黎世博会开幕启用；阿姆斯特丹地铁是荷兰首都阿姆斯特丹的地下铁路系统，于1977年开始启用；1904年10月27日，纽约市第一条地铁南北干线正式通车。故本题选D。
| 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. |
Which of the following best expresses the main idea of Paragraph 2
A．Because of their characteristics as double organisms, it is difficult to classify lichens.
B．Over 15,000 varieties of lichens have been identified.
C．Double organisms should always be classified as separate species.
D．Taxonomists always find it difficult to classify new species of plants.