选
a
regarded
这是过去分词做状语表示被动和已经。所以不用b.
having
been
regarded
因为这是现在分词完成时态的被动式。表示某一动作已完成或持续了多久。常有一个时间状语在分词后。下面给你两个例子你会明白。
given
more
time
,we
could
do
it
better.=if
we
were
given
more
time
,we
could
it
better.
having
been
taught
several
times
,he
still
couldn't
answer
the
question.=
although
he
had
been
taught
several
times
,he
still
couldn't
answer
the
question.
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