I mean that he cares only for himself 是一个完整的句子!你用which的话,它是不是多余?I mean that he cares only for himself by which等于 I mean that he cares only for himself by what i have said(He is to...
by which 这里是非限制性定语从句, which可以代指前面提到的一整句话。但是通常说“which means he cares...”而by which表示从“上句话里得出用来”,“从那句话里看到”的意思,加上后面的I mean,就是:“I mean by which ...”才是正确的。呵呵