With the changes in the world's climate, dinosaurs died, but many smaller animals lived on. It was the survival of the fittest. 隨著世界氣候的變遷,恐龍絕跡了,但許多較小的動物卻繼續活了下來。 這就是適者生存。
牛津高階第八版
美國韋氏詞典
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維基百科 (自由的百科全書)