The snake stone in the novel is ______.

参考解析：

细节理解题。根据The turning point中“The turning point in the story comes while James’ foster parents are away in London, and he wonders about the identity of his birth mother. The only clue he has is a fossil, ‘the snake stone’ which she left behind along with a note on which she had written: ‘Take good care of Sammie.’”可知，故事的转折点发生在詹姆斯的养父母不在伦敦的时候，他想知道亲生母亲的身份。他唯一的线索是一块化石，“蛇石”是她留下的，还有一张纸条，上面写着：“好好照顾珊米”。由此可知，the snake stone是James生身母亲离开留下的识别身份见证物。故选C。