prove做系动词

A首先这是一个完整的句子,所以不缺少谓语,要填上一个非谓语.而计划被证明,proved是过去分词有被动的意思.
第二种理解是proved作系动词,Their plan作主语,后面的不定式作表语

prove
作"证明是;结果是;事实说明"解时,用作连系动词,可用于以下句型:
1.prove+形容词
The
handbook
proved
most
useful.这本手册证明很有用.
The
medicine
proved
satisfactory.结果证明这药疗效令人满意.
2.prove+名词
She
proved
a
very
strict
teacher.结果证明她是一位非常严格的老师.
His
efforts,
however,
proved
a
failure.但他的努力结果都失败了.
3.prove+介词短语或副词
Perhaps
this
book
will
prove
of
some
use
to
you
in
your
studies.也许这本书会对你的研究有用处.
The
power
station
was
completed
and
proved
up
to
standard.这座发电站建成了,证明质量符合标准.
4.prove+动词不定式
As
time
went
on,
Einstein's
theory
proved
to
be
correct.随着时间的推移,爱因斯坦的理论证明是正确的.
She
may
prove
to
be
the
most
suitable
person
for
the
job.结果她可能是最适合干这项工作的人.