定语从句怎样判断关系代词是做主语还是宾语

这个问题其实你明白。一般来说
定从中的谓语动词前没有任何名词代词，那么关系代词就是主语。谓语动词是及物动词，后面又没有名词代词作宾语，也就是缺宾语，那么关系代词就是宾语。
上次你所给骆驼的句子
因句子不完整，我就没回答。
不要把现行词在整个句子中所充当的句子成分
和它被代以后在定从中所充当的成分
搞混。
也就是说
先行词可能是主语
但被代以后在定从中可能是宾语。
如the
horse
that
he
had
had
three
legs.他的马有三条腿。

He
is
the
man.
He
came
here
last
week.
He
is
the
man
who
came
here
last
week.
(该句中的“who
came
here
last
week”为定语从句，修饰“the
man”，很明显，从句中的“who”是“came
back”动作的发出者，所以“who”在从句中充当主语。)
She
is
the
woman.
I
served
her
yesterday.
She
is
the
woman
I
served
yesterday.
(该句中的“I
served
yesterday”为定语从句，修饰“the
woman”，其实，定语从句中省掉了关系代词“who，whom或that”。关系代词在定语从句中作宾语时，可将其省略。完整的句子应为“She
is
the
woman
who
/
whom
/
that
I
served
yesterday.
”如果将从句部分的关系代词代入句中的话，应为：I
served
who
/
whom
/
that
yesterday，很明显，从句中的“who
/
whom
/
that”是“served”动作的承受者，所以关系代词在从句中充当宾语。)
They
are
the
books.
I
bought
the
books
last
year.
They
are
the
books
I
bought
last
year.
（该句和第二句用法相同，关系代词which
/
that因在定语从句中充当宾语，被省略了，能看明白吧？其实完整的句子应该是：They
are
the
books
which
/
that
I
bought
last
year.
关系代词代入定语从句中，则为：I
bought
which
/
that
last
year.
能看出“which
/
that”充当的是宾语吧。）
好了，就解释这么多，相信你能看懂的。祝你英语学得越来越好！