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.
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试题解析
细节题。题干中的关键词为pioneers，该词出现在第一段最后一句，该句中的伴随状语提到appearing in barren rocky areas and starting the formation of soil in which mosses, then ferns, and then other plants can take root （它们在贫瘠的多岩石地区生长，开始了土壤的形成，之后各种植物才得以据此生根），由于前一句指出（地衣是生长在南极洲的植物之一），可知选项C（它们是首先在南极洲生存的植物）符合文意。
