请问,---- you don't know the rule won't be a sufficient excuse

请问,____ you don't know the rule won't be a sufficient excuse for your failure.a. it is b. that c. because d. what请帮我分析一下,这几个选项对的,为什么对,错的错在哪里.O(∩_∩)O谢谢大家!可是我看网上说，it ,that ,what 都可以引导主语从句啊