Teacher：We all know that beat causes an object to expand an cold cauese it to contract. Now，can anyone give me a good example?

　　John：Well ，in the summer the days are long，and in the winter the days are short.

　　老师：我们都知道热胀冷缩的道理。现在，谁给我举个例子?

　　约翰：嗯，在夏天天都长，在冬天天都短。