定语从句中关系代词that +be动词is时的省略，像下面: We had a lon

Question

定语从句中关系代词that +be动词is时的省略，像下面:

We had a long debate about what to do next中本来应是完整定语that is about what to do next，但省略了that is吗？可这样吗？如果可以，这是什么规则呢？

Answer 1

两个的句子结构不同，第一个只有about what to do next是介词短语，后一句若改为that is about what to do next则为定语从句，修饰前面的debate。追问

那如果句子是 定语从句中关系代词that +be动词is时的省略，像下面:

We had a long debate that is about what to do next，句子中的that is可以省吗？

那如果句子是
We had a long debate that is about what to do next，句子中的that is可以省吗？

可以回答吗