21. Carrots and Potatoes 胡萝卜和甜土豆里有种物质x,常吃胡萝卜和甜土豆的人癌症得病率低,结论x有助于防止癌症,问要evaluate下列哪项?
狗主答案: 我选胡萝卜和土豆里是否共有除x外的某种物质,在别的常见食品里是没有的 P: Eating carrots and Sweet potatoes have mineral X C: Eating Sweet potatoes and carrots will reduce the chances of having cancer