"that" 可以用来指代先前提到的事物、概念、现象、人或物品等，以避免重复或简化句子结构。例如：

- Jenny bought a book yesterday. She found that it was a bestseller.（Jenny 昨天买了一本书。她发现它是一本畅销书。）

- The weather was so hot that it made everyone feel tired.（天气太热了，让所有人都感到疲倦。）

- I was looking for my purse, but I couldn't find it. That was really frustrating.（我在找我的钱包，但找不到它，真让人沮丧。）

在这些例子中，"that" 都代指了之前提到的事物或概念。