宾语从句that与which 区别是什么？

宾语从句中that一般在口语中常可以省略，在句中不做成分。
但是which在句中充当成分，一般不可以省略。
例如：I said (that)he was right
He asked me which was his
that引导宾语从句无意义，不充当句子成分常省略。但下列情况除外：
①．介词宾语从句的that不能省略。
He is a good studentexcept that he is a little careless
②．and连接的两个从句，两个从句的that不能省略。
He told me that he hadtwo sons and that they both had gone to college.
③．在动词+it+宾语补足语+宾语从句结构中，that不省略。
I heard it said that hehad gone abroad
We found it impossiblethat he could finish it in such a short time

1
that
\which在代物时常常可以通用,但有时只宜于用which
,不用that
(1)
关系代词前有介词时.
This
is
the
hotel
in
which
you
will
stay.
(2)
如有两个定语从句,其中一句的关系代词是that,另一句宜于用which.
Let
me
show
you
the
novel
that
I
borrowed
from
the
liberary
which
was
newly
open
to
us.