They want to make it clear to the public   （）     they do an important job.

题目解析[填写题目解析]： 题目：They want to make it clear to the public _____ they do an important job. 答案：C. that 解析：这道题是一个宾语从句的考察。句子的主干是"They want to make it clear"，宾语从句用于说明"clear"的内容是什么。在宾语从句中，需要使用连接词"that"来引导。因此，正确答案为C选项。