Teacher：We all know that beat causes an object to expand a 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。