He is good at English，__________we all know.
A.that B.as C.whom D.what
He is good at English，__________we all know.
A.that B.as C.whom D.what
B
as作关系代词可以单独用来引导非限制性定语从句。这时as所指代的不是主句中某个名词，而往往指代整个主句的含义。as在从句中可以作主语、宾语。从句可放在主句后，也可置于主句前。在本句中,as作宾语。