北方人喜面食，南方人喜食米饭，造成这一差异的主导因素是（　　）

    Alice was very worried about her dad. For some time now she had noticed he was 1 his hair. One day, she asked him, “Daddy, every day you have less hair.2 is that?” Her father smiled and said, “It's the hair thief. He visits my head during the night when I'm 3. One by one he 4 out my hair, as much as he likes.”

    This worried Alice but she was 5 to help her father. That very night she stayed 6 as long as she could. When she was 7 her dad and mom had fallen asleep, she took a hammer and went straight to their bedroom. She walked carefully in order not to make any 8. She didn't want the hair thief to hear her. Then she began carefully 9 her father's head. When she arrived at her father's side, she began looking at his head,10to catch the hair thief as soon as he appeared. Before long, she saw a shadow on it and 11 all her strength, she swung the hammer down.

    Thwack! Her father 12a loud cry. The lump(肿块) on his head was big and growing.13 with shock, he turned the light on and saw Alice waving her hammer in the 14 with her hands. “Daddy, I 15 got him. I thought I 16 him, but it looks like he escaped!” said Alice. At the same time, the mother woke up. She 17laughing when she knew what had happened.

    So Alice's father had to 18to her that the hair thief didn't exist, and that losing hair is something that just happens 19 to most daddies. And Alice still worried about her daddy, but she no longer waited for the hair thief.20 , she bought her daddy a very nice sleeping hat.

根据材料，运用所学知识回答以下问题：

材料一：维护社会公平是一个全局性的问题和一项长期性的任务，不仅要运用经济的手段，而且要运用法律、行政等多方面的手段，进行综合治理。

材料二：长期以来，中央一直把解决社会公平问题作为一项重要的政策，对于低收入群体、贫困群体更是给予了特殊的关怀，采取了一系列政策措施，如扶贫开发、加强社会救济、支持慈善事业、完善社会保障制度、逐步提高最低生活标准等。这些政策措施的实施，对于改善低收入群体、贫困群体的生存状态和生活状况起到了积极作用。中央还决定，免除农业税，免除义务教育阶段的学杂费，加大对农村教育、卫生事业的投入。