题目

Going home for Christmas is a tradition of the holiday season. No matter where you may be the rest of the years, being at “home” with your family and friends for Christmas is a “must”. The Thanksgiving and Christmas holidays are the busiest times of the year at airports, train stations and bus stations. It seems that all America is on the move and Americans are on their way to spend the holidays with their loved ones. This means that the house will be full of cousins, aunts and uncles that might not see each other during the year. Everyone joins in to help in the preparation of the fes我国研制的一种聚乙烯材料，超过40℃时完全熔化，低于15℃时完全凝固．有人设计，把这种材料制成小颗粒，掺在水泥中制成地板或墙板，在昼夜温度变化大的地区用这种地板和墙板修筑房屋，便可以起到调节室温的作用．请你解释，这种设计的原理是什么？