who is the girl （ ）is standing at the gate?A that B who C what D which

主句是以who开头的特殊问句时,只能用that作引导词.关系代词who，whom，that，which在从句中作介词宾语时，不可省?who、that 也能做介宾？如果介词放在引导词之后时不能省，直接放在介词之后时，不能用who或者that。