I can’t tell one twin from the other. 我分不出雙胞胎中誰是誰。
I spoke to both of the twins this morning. 今晨我與兩個雙胞胎都談了談。
類似地，parent指父母之壹，即指父親或母親，要表示父母雙親，應用復數parents。比較：
A half-brother is brother with only one parent in common with another half-brother指同父異母或同母異父的兄弟。
The parents named their baby Tony. 父母給他們的孩子取名托尼。
（摘自《英語常用詞多用途詞典》twin詞條，金盾出版社）