(1)当关系代词紧跟介词,作介词宾语时,只能用which或whom,不能用that。但当介词位于从句句末时,仍可用that或省略。如:
This
is
the
house
about
which
we
wrote
to
you.
Do
you
know
the
man
to
whom
your
brother
writes?
I
have
read
the
book
(which
/that)
you
told
me
about.
(2)当先行词是all,
everything,
something,
nothing等不定代词,或被first,
last,
only,
few,
much,
some,
no,
any以及形容词的最高级修饰时,只能用that,不能用which。如:
All
(that)
they
needed
were
qualified
workers.
This
is
the
most
difficult
book
(that)
I
have
ever
read.
(3)在非限制性定语从句中,只能用which,
who,
as,不能用that。非限制性定语从句既可修饰先行词也可修饰整个主句,往往起补充说明的作用,并有逗号与主句隔开。如:
He
was
ill
for
a
month,
which
set
him
back
a
lot
in
his
work.
I
want
to
buy
a
house,
which
has
a
garden.
有用请采纳,谢谢!
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