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  3. Lichens may grow on the bark of a tree in a steaming tropical rain forest, o

Lichens may grow on the bark of a tree in a steaming tropical rain forest, o

游客2023-12-27  39
问题     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. [br] Why does the author call lichens pioneers?
选项 A、Because they developed so early in the history of the planet.
B、Because of their primitive structure.
C、Because they prepare soil for other plants.
D、Because they were the first plants to live in Antarctica .
答案 C
解析 细节题型见第一段最后一句的伴随状语：appearing in barren rocky areas and starting the formation of soil in which mosses，then ferns，and then other plants can take root(它们出现在荒芜的多岩石地区，使得土壤开始生成，然后各种植物才得以据此生根)可知C为答案。
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