什么时候用this is my sister,什么时候用she is my sister?

This is my friend 和 These are my sist 改成否定句怎么改啊,急... 什么时候用she is my sister ?什么时候用this is my sister?急!急! 什么时候用this is my sister,什么时候用she is my sister? 什么时候用Here 什么时候用This is 用所给的介词填空介词：in,on,at,of ,to ,for1.This is the classroom which he studied more than ten years ago.2.The famous player can play two chess games one time.3.He and his twin brother have a lot common.4.I'll come condition that my sist 四年级英语专项练习 对划线部分提问:1.I get up at seven.划线词：at seven.2.Mr Black is my English teacher.划线词：Mr Bkack.3.That is her dog.划线词：her.4.This is my sist 根据句意及首字母提示完成单词.Mary is my a().She's my father's sister.用所给词的适当形式填空.These()[be] my rulers.Those are her ()[sister].Her()[parent]are in Beijing.()[her] is Kate's mother.()[he] mother is my mother's sist 《This is my This is my Miss li,this is my father.为什么用this is 选出适当的句子补全对话A.Of course,you can.Here you are.B.What's it about?C.Oh,it is really interesting!D.I want a magazine.--What do you want?-1.---How about this one --2.--About all insects like ants.--3.--Can I bring it to my little sist This is my book用whose提问 this is my skirt(用mine改写) this is my life my This is my This is my THIS is my this is my This is my