1.Is this your sister? No, it isn’t.
Is she your sister? No, she isn’t.
2.This is my friend. These are my friends.
That is my brother. Those are my brothers.
3.Thanks for the photo of your family. Here is my family photo.
photo of your family = your family photo
可数名词单数变复数：一般情况下加s, book-books， 以s, x, sh, ch结尾的加es
watch-watches 以辅音字母加y结尾的，把y改为i再加es boy- boys, family-families 以o结尾的有生命的加es, 无生命的加s, tomato-tomatoes, photo-photos