问题描述：
the old lady has three sons,(),luckily for her,works as a doctor.A.none of whom
the old lady has three sons,(),luckily for her,works as a doctor.
A.none of whom B.one of whom C.either of whom D.all of whom
the old lady has three sons,(),luckily for her,works as a doctor.
A.none of whom B.one of whom C.either of whom D.all of whom
问题解答：
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