____is well-known is ____light travels faster than sound.
问题描述：
____is well-known is ____light travels faster than sound.
A.it,that B.what,/ C .As,that D.whta,that
选D,为什么不选其他的,
答
要表达“人人皆知的是,光的速度比声音的快.”
只有D合适.
其他的,如果是A项,应该是：
It is well-known that light travels faster than sound.（it 作形式主语）
如果是C项,则是：
As is well-known,light travels faster than sound.（as 作关系代词）