Question

Yes,she is.She is my sister (上一句是什么) Is she your mother? (下一句是什么）

Answer 1

Is she your sister? 回Yes,she is.She is my sister .
Is she your mother? 回 Yes,she is.She is my mother.
或者NO,she isnt.She is my sister.

Answer 2

1.Is she your sister?
2.Yes,she is .(She is my mother)可加可不加

Answer 3

Is she your sister? (一般疑问句，把be动词提前即可）
Yes, she is. She is my mother. (主谓宾形式）
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主 谓语 宾语