@ryouru: "A sister" is one person. "A twin sister" is a type of sister. "Sisters" means more than one sister. "Twin sisters" means two sisters who were born on the same day.|"My twin sister is a little taller than me." "I have a twin sister." "I have twin sisters." Better yet, what is that you're trying to say?|All. She is my twin sister. Those two are twin sisters. She has a twin sister. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.