介词+which的定语从句什么时候可以用where，when等替换？

Question

如下面三句能否，why？
This is the town in which they live.
China has a long history during which many of the world's greatest poets were active.
The school in which he once studied is very famous.

Answer 1

简单的说，如果把介词提前的话，就要用介词+which的形式，因为关系副词前面是不能加介词的。
就像第一句和第三句live和studies的介词in如果放在一起，前面就能用where，
this is the town where they live in
the school where he once studies in is very famous.

PS: 定语从句去掉之后原句还是个完整的句子，这样的结构才正确，如果你去掉定语从句之后原句只是个短语了，你这个句子就造错了。
正确：This is the school (which is very famous).
错误：The beautiful school (which is also very famous).

Answer 2

1
he
has
lost
the
key
to
the
drawer__a
/
b__the
papers
are
kept.
a
where
b
in
which
c
under
which
d
which
你好。选项a
和b
都是正确的,都指代方位，表示“在-
-
-里面”。
the
drawer
in
which
==where
the
papers
are
kept
2
the
train
_b
_she
was
traveling
was
late
.
a
where
b
in
which
c
under
which
d
which
这句只有b是正确的，因为
in
这个介词在这里解释为“乘坐”，不解释“在--
-
里面”。ok?

Answer 3

关系副词引导的定语从句可以用“介词＋关系代词”替换。比如你说的那三个句子中的“in which”都可以用“where”替换…
当在“介词＋关系代词“引导的定语从句中，关系代词只能用whom(指人）和which（指物）