![](https://cos-cdn.shuashuati.com/pipixue-wap/2020-1230-1107-53/ti_inject-812ce.png)
把下列句子变成复数形式。 ①This is my sister. __________________________________ ②That is his brother. __________________________________ ③What is this? __________________________________ ④Is this your friend? __________________________________ ⑤That isn't a book __________________________________