熱脹冷縮

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.

老師：我們都知道熱脹冷縮的道理。現(xiàn)在，誰給我舉個例子？

約翰：嗯，在夏天天都長，在冬天天都短。