托福听力official31 Paragraph 5 supports which of the following statements regarding the importance of fires in maintaining savannas? 答案解析

用 importance of fire 去定位，对应部分从 but in experimental are as protected from fire 开始，后面的内容都对其重要性进行了解释：But in experimental areas protected from fire, a few perennial grass species eventually come to dominate, outcompeting all others. Evidence from other studies suggests that exclusion of fire results in markedly decreased plant-species richness, often with an increase in tree density. 从这两句话可以看到，如果没有火来保持 savannas，那么就很少有 perennial grass species 可以 outcompeting 其他的种类，从而减少了 plant‐species 的丰富，而树的密度则会更大。对应了 D 的描述。ABC 选项都在原文未提及。