在定语从句中，that前为什么不能加宾语，而which可以？

通常讲，先行词是人时，作定语从句主语（定语从句动词的发出者）用who引导，而在who引导的特殊疑问句中必须改为that；作宾语（定语从句动词的承受者）选who(m),that均可以、但介词后只用whom, eg. This is the boy who often helps me with my art. This is the boy who/whom/that I often help. This is the boy from whom I often learn. 先行词是物时，作定语从句 作主语/宾语 用which/that 引导，而在which引导的特殊疑问句中必须把which改为that,；先行词是物时，作定语从句 作主语/宾语且 先行词中含the one,the only, the same, none, nobody,little ,few, nothing,序数词最高级时必须把which改为that，但定语从句动词为不及物动词时，介词可前置，用介词＋which，也可后置用which/that 引导定语从句。 eg. This is the factory in which I've worked for 10 years. This is the factory which/that I've worked in for 10 years. This is the factory where I've worked for 10 years. 先行词是地点状语时，(既不是 主语也不是宾语 ）用where、介词＋which引导定语从句， 先行词是时间状语时用when、介词＋which引导定语从句! 以上讲解是我一个一个地打出了的，没有从任意网页复制！而且也希望你看了后能明白定语从句引导词的选择！