定语从句怎么判断关系词做什么成分The boy who I know studies best in his class 这句话从句中有I做主语 那么who就肯定是宾语 那这句话He didn't become a person who his father wanted him to be 从句中有his father作主语who为什么成了表语?还有第一句我发现study用了单三 是因为先行词吗?从句时态要跟先行词一致么?

1、The boy who I know studies best in his class 中，studies 是主句的谓语，当然取决于主句的主语，主句的主语是the boy，三单，故主句的谓语要与主语保持一致，即用studies。
此外，定语从句的谓语动词的单复数要跟先行词一致的。至于时态，则要看从句具体表达的语境来定。从句的时态与主句的时态并无直接的关系，是互相独立的。
2、He didn't become a person who his father wanted him to be .在这个定语从句中，先行词是person，关系代词是who，代替先行词 person，从句的主语是his father，宾语是him，who做表语，逻辑上是his father wanted him to be (the) person。
另：学习定语从句时须注意关系代词的“三个”作用，即
（1）替代作用：代替先行词的作用
（2）连接作用：连接主句与从从句的作用
（3）成份作用：在从句中充当相应的句子成份的作用

其实很简单 从句只要将句子还原回去就行
第一句 i know the boy studies best所以用单三
第二句 to be a person 作为表语

1.He didn't become a person who his father wanted him to be .在这个定语从句中,先行词是person,关系代词是who,从句的主语是his father,宾语是him,who做表语,逻辑上是his father wanted him to be who.
2,The boy who I know studies best in his class 中,studies 是主句的谓语,当然取决于主句的主语,主句的主语是the boy,三单,故用了studies.一般来讲,这与先行词无关的.只不过这里的先行词刚好就是主语.
此外,定语从句的谓语动词的单复数要跟先行词一致的.至于时态,则要看从句具体表达的语境来定.从句的时态与主句的时态并无直接的关系,是互相独立的.
祝你进步.