Which of the following statements is TRUE?

参考解析：

细节理解题。根据第三段第三、四句“...they seem to suggest that they ate almost anything that they came across. The point is that they had big teeth that were really sharp, and that was even relative to the size of their jaws were relatively large, so they were really predators.”可知，古鲸鱼可能会吃掉他们遇到的所有生物，而不是海豚，排除A项；关键是它们的牙齿确实很锋利，甚至与颚的大小有关，而未提及比下颚更大，排除B项；根据第二段“So, the oldest whales that we know, these are the ancestors not just of the great whales like the blue whale and the humpback whale, but also of all of the dolphins in the sea today, they had fairly big teeth.”可知，最古老的鲸鱼不仅是蓝鲸和座头鲸等大鲸的祖先，而且是当今海中所有海豚的祖先，它们的牙齿相当大，C项表述正确；我们知道古鲸鱼有巨大的牙齿，并非蓝鲸，排除D项；结合题干选择表述正确的一项，故选C。