题目

 阅读理解。阅读下列材料，从A、B、C、D四个选项中选出最佳答案。 All through the winter, the Esquimaux(爱斯基摩人) live in houses made of snow. These small houses are very clean and white when they are new. They can soon turn dirty, but pieces of fresh snow make them new again.    Sometimes the Esquimaux build their small houses with the wood that they find along the seaside. However, they aren’t always so lucky. When they can’t get wood, they use the snow. It is so cold that the snow becomes very hard, so the small houses are strong enough in the wh12．分解因式：（1）4ax2-ay2（2）16-8（x-y）+（x-y）2．