參考：
主語從句
定義:在句子中擔當主語的是壹個從句,這個從句就叫做主語從句。
主語從句是在復合句中充當主語的從句，通常放在主句謂語動詞之前或由形式主語it代替，而本身放在句子末尾。
1、主語從句常用it作形式主語，壹般常用句型為：
It
is+{名詞/形容詞/過去分詞}+主語從句例如：
It
is
still
a
question
whether
she
will
come
or
not.
It
is
strange
that
you
should
like
him.
It
is
still
unknown
which
team
will
win
the
match.
另外，還有壹些比較多見的結構：
It
turned
out
that……；
It
has
been
proved
that……;
It
happened/occurred
that……；
It
is
well-known
that……等等
2.
用it
作形式主語的結構
(1)
It
is
+名詞+that從句
It
is
a
fact
that
…
事實是…
It
is
an
honor
that
…非常榮幸
It
is
common
knowledge
that
…是常識
(2)
it
is
+形容詞+that從句
It
is
natural
that…
很自然…
It
is
strange
that…
奇怪的是…
(3)
it
+不及物動詞+that從句
It
seems
that…
似乎…
It
happened
that…
碰巧…
(4)
it
is+過去分詞+that從句
It
is
reported
that…
據報道…
It
has
been
proved
that…
已證實…
主語從句不可位於句首的五種情況
(1)
if
引導的主語從句不可居於復合句句首.
(2)
It
is
said
,(reported)
…結構中的主語從句不可提前.
例如： It
is
said
that
President
Jingo
will
visit
our
school
next
week.
(3)
It
happens…,It
occurs…
結構中的主語從句不可提前.
例如： It
occurred
to
him
that
he
failed
in
the
examination.
(4)
It
doesn’t
matter
how/whether
…結構中的主語從句不可提前.
例如： It
doesn’t
matter
whether
he
is
wrong
or
not.
(5)
含主語從句的復合句是疑問句時,主語從句不可提前.
例如： Is
it
likely
that
it
will
rain
in
the
evening?
妳的提問是其中(2)
It
is
said
,(reported)
…結構中的主語從句不可提前.
例如： It
is
said
that
President
Jingo
will
visit
our
school
next
week.