I don't know what the reason can be.和 I don't kno

I don't know what the reason can be.和 I don't kno
I don't know what the reason can be.和
I don't know what is in the stockings.
这两句话中为什么一个宾语是完整的疑问句一个却是倒装?可能的话最好说明一下What在两句中的成分.