The difference between a pearl and a cultured pearl is the nature of the ______.
A.color
B.introduction of the irritating impurity
C.coating material
D.irritating impurity
参考答案:B
解析:[分析] 细节题型。 文章第二句(A pearl is the response of a marine…a live mollusk.)指出:天然珍珠中的刺激性的杂物是偶然进入体内的(accidentally introduced into its body);而人工培育的珍珠中的杂物是人为加入的(the intentional insertion);所以选项B正确。