氟泰[氟化钠（NaF）、二氧化硅]是牙膏的主要成分，其作用不仅能帮助防止牙齿表面蛀牙，而且能显著降低根部蛀牙的发生率，这里的氟化钠和二氧化硅都属于（　　）A．混合物B．氧化物C．单质D．化合物
氟化钠是由钠元素和氟元素组成的纯净物，属于化合物；二氧化硅是由硅元素和氧元素组成的纯净物，属于化合物．故选D．
为您推荐：
化合物是由不同种元素组成的纯净物；化合物包括酸、碱、盐、氧化物等．
本题考点：
单质和化合物的判别．
考点点评：
解答本题要掌握物质的分类方法，只有这样才能对各种物质进行正确的分类．
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