问题描述：
tom is six and he is __his sister Mary.How old is Mary?--three
A.twice as older as
b.two years older than
c.three years yonger than
d.as old as
选A的原因
A.twice as older as
b.two years older than
c.three years yonger than
d.as old as
选A的原因
问题解答：
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