The story of the group traveling in the desert was —— we had never heard before.

The story of the group traveling in the desert was —— we had never heard before.
A：that B：it C：one D：the one
为什么选one,语法上分析分析呢 还有 为什么不是定语从句呢?为什么不选that呢,这句话有没有其他讲法呢 比如 The story of the group traveling in the desert was one which we had never heard before,