Is she your sister?怎么变成复数形式

Is she your sister?怎么变成复数形式 is that your sister改为复数形式,怎么改? Is she your sister?改为复数怎么改? She said:"Your sister is fine"怎么变成间接引语? This is your sister.改为复数形式 she is a good student.改为复数形式 Is your sister quiet?肯定回答 She is her aunt.变成复数形式 将下列句子变成复数形式：This is my sister. Is she your mother?复数形式 Is she your friend的复数形式 She is my sister（改为复数形式） she is your sister怎么排列