英语单选题

答案是D,what引导主语从句并作主语从句的中的主语.
选项AC,that引导名词性从句时不能作句子成分故错
选项B,it.是形式主语须把第二个is去掉
如果用 as 则是非限制性定语从句须把 is that去掉换成逗号
_what is known to us all is that the Chinese goverment has spared no efforts toprotect people from fake food
=it is k