题目

根据短文内容, 回答下列问题。 I'm Anna. Today is Sunday. I don't need to go to school. I like cooking with my mom on Sunday. I can cook noodles, cakes and fish well.After finishing my homework, I find there is little food in the fridge (冰箱). So I go to the supermarket with my mom. There are many kinds of food in the supermarket. My mom likes Chinese food very much. She buys dumplings and some meat-balls. I enjoy Western (西方的) food, so I buy some salad and bread. I want to have hamburgers, too. We also buy some bananas. They look very good. All the food is 122 yuan. I give若区间[x1 ， x2]的 长 度 定 义 为|x2﹣x1|，函数f（x）= （m∈R，m≠0）的定义域和值域都是[a，b]，则区间[a，b]的最大长度为（ ）A.B.C.D.3