It is Sandy's sister中的it怎么解释

Who is Sandy's sister? it is sandy 's pencil 对 sand'S提问 who's singing over there?______is Sandy's sister.A That B It 可以问Sandy's sister is who? How was Sandy's weekend? Was it fun?怎么回答 There is () umbrella behind the door.It isn't Sandy's.It's ( It’s/is it/it is怎么读? ()bedroom is it B:It's my sister's.（疑问词） 改下列句子中的错误：1 It's time to lunch.2 Is your sister have lunch a What ___ this ring?Is it yours,too?No,it is my sister's. what _____this ring?is it yours,too?NO,it is my sister's whe She said it's good for you.中的it's是it is 还是it was,