This duck was thin before. 这是一个有be动词的陈述句
变一般疑问句步骤:
(1)把be动词“was”提前
(2)句尾打问号“?”
整理:Was this duck thin before?
否定回答:No,it wasn't. (问句中主语是the duck, 回答的时候用 it 指代)
希望能帮到你~~
正常的是改为一般疑问句和并作否定回答都行
Was this duck thin before?
No,it wasn't.
Was thin duck thin befove?
No,it was not.