24.___________ is known to all, the earth moves around the sun once a year.
A That B. As C. What D. It

[B]本题考查的是as 引导的非限制性定语从句，as 指代后面的整个句子，句意为：正如大家所知道的，地球一年绕太阳转一圈。这种表达方式已经相对固定了如果此处填it ,这句话应该这样表达：It is known to all that the earth moves around the sun once a year. that the earth moves around the sun once a year是主语从句后置，it 只是个形式主语。选项that 不能引导非限制性定语从句，what不能引导定语从句。