"That is the reason why..." 是一种常见的英语表达方式，用来表示某件事是另一件事的原因。这种表达方式来源于英语中的连接词 "that"，用来引入一个原因或结果。
下面是一些例句:
The weather was bad, that is the reason why we didn't go to the park. (天气不好，这就是我们没去公园的原因。)
I was tired, that is the reason why I didn't go to the party. (我很累，这就是我没去聚会的原因。)
The store was out of stock, that is the reason why I couldn't buy the book. (商店没有货，这就是我买不到那本书的原因。)