57.They asked the government to make ------- clear to the pu

此处选B
it作形式宾语,后接that引导的宾语从句,对形式宾语的内容进行修饰补充
*此处省略了引导词that
在从句中what作为引导词引导了主语从句,what they did充当从句部分that what they did was right的主语部分.
所以此句应为They asked the government to make it clear to the public (that) what they did was right.
希望能够对你有所帮助^ ^