This is my sister?怎么变复数形式?代词my用变复数吗?

This is my sister?怎么变复数形式?代词my用变复数吗? this is my my friend(变复数) my sister name变复数 This si my pen pai.(变成复数形式)怎么变? This is my sister.改为复数形式、 Sam is my friend.(变为复数形式)怎么变 That is my grandmother.怎么变复数 请问单数句变复数句,句中的人称代词跟着变吗?例如：This is my friend,在变为复数句时,是These ar This isn't my brother 变复数形式 she is a teacher.变复数 it is a pen.变复数 this is my is this that 变复数怎么变 将下列句子变成复数形式：This is my sister.