SAT2011年5月真题语法问题section 5 第8题 正确答案是C，为什么不是to be diagnosed

Question

如题所述

Answer 1

这个问题提得很好。这涉及到不定式的逻辑主语问题。
不定式并不像现在分词或过去分词那样表示明显的主动或被动关系,它的逻辑主语只能根据句子的意思去慢慢体会找出。不定式用主动结构表被动的形式总结如下:
1)
sb
have
sth
to
do
(不定式的动词所表动作由句子主语完成)
如:
I
have
many
flowers
to
water.(我给花浇水)
2)
sb/sth
be
adj
to
do
(介词).(实际上省略了for
sb.不定式的逻辑主语是sb.)
如:
English
is
diffilult
to
learn.
She
is
hard
to
work
with.
3)
There
be
sth
to
do(但也可使用to
be
done)(同样省略了for
sb.不定式的逻辑主语是sb.)
如:
There
is
still
a
lot
of
work
to
do.
4)
with
sb/sth
to
do
sth(不定式的逻辑主语是后面句子的主语)
如:
With
a
lot
of
work
to
do,
I
can't
go
out
to
play
with
you
now.
再如:
With
you
to
help
me,
I
can
finish
the
work
easily.
(当然该句只是用来和上句对比说明该动作并未发生,它并不是不定式主动表被动用法)
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