有的时候不要改为or 我都有点糊涂了．

Does Nancy have a brother or a sister?

Does Nancy have a brother or a sister? 有关是可以的吧．似乎它也可以回答成Nancy has a brother and a sister．

Does Nancy have a brother or a sister?

否定句或一般疑问句中的AND要变成OR的!
比如NO EATING OR DRINKING是禁止吃喝(饮食)的意思, 而不是禁止吃或者喝. 不能单纯地看到OR就一定认为是选择疑问吧?
这里Does Nancy have a brother or a sister?还是应该解释为 南希有兄妹吗?
个人意见!

Does Nancy have a brother or a sister? 我认为是对的

Dose Nancy have a brother or a sister ?
应该是这样的吧！！

是吧。是6b的第一单元的句型。