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twins; twin
二子が生まれると聞いて家族が喜んだ。
The family was delighted to hear twins were born.
二子は顔がそっくりで見分けがつかない。
The twins look so alike that you can't tell them apart.
二子の兄弟はいつも一緒に遊んでいる。
The twin brothers are always playing together.