姐姐是
the elder sister───姐姐
elder sister───姐姐，姊姊；[法]姐姐; 姊; 媭
an elder sister───姐姐
sister is───姐姐是
elder───n.长辈，年长者；比……年长的人；（基督教会中的）长老；（部落等群体的）头人，族长；接骨木；n.(Elder)（美）埃德（人名）；adj.年龄较大的；（用于人名前或后，指同名者中）年龄较大的一个；资格老的
cato the elder───老卡托
sister───n.姐妹；（称志同道合者）姐妹；修女；护士；adj.姐妹般的；同类型的
the sister years───姐妹年
older elder───年长的长者
Elder sister is civilized men, all the dirty words have sterilized with saliva.───姐是文明人，所有的脏话已经用唾液消过毒。
The twins are five years old, and their elder sister is eight.───两个双胞胎今年五岁，他们的姐姐今年八岁。
My elder sister is the center of my life. I never find the absence of love, friendship or guardian till I am with my sister.───我的姐姐是我生活的中心。和姐姐在一起为止，我从来没有缺少过爱情、友情和保护。
The elder sister is missing a pair of glasses and I am very angry, but the mother accompany her and went together with a pair of glasses.───姐姐不见了一副眼镜，我很生气，但是妈妈陪她又去配了一副眼镜。
Conclusion: The twin girls originate from dizygotic and the extra chromosome 21 of the elder sister is from nondisjunction during the first meiotic division of the mother.