Since there is such an abundance of food in the sea, it is understandable that some of the efficient, highly adaptable, warm-blooded mammals that evolved on land should have returned to the sea.

• 既然海洋中有如此丰富的食物，一些原本在陆地生存的高效率的、适应性强的暖血型动物返回海洋生存是不难理解的。