题目内容：

the plan ------- they came up with was very good.A this B it C \ D what

优质解答

C
这是定语从句,省略了关系代词
the plan 【that/which】they came up with was very good.同时that/which 做with的宾语
翻译：他们提出的计划非常好
AB不能引导从句,D不能引导定语从句