First, thank you Edwin Ashworth and RegDwigнt♦ for your comments. I was able to learn and recognize my mistake, obscuring the point of question.
Here is as to I've wanted to discuss about:
- He was uncertain as to which road to take.
(Example given by Ediwn Ashworth)
Obvious though this is for you, I, as not a native, cannot get how this can possess the meaning, about. I suppose that these two prepositions, as and to, independently have several meanings depending on context they involve - meaning, roughly, such as "like", "while", et cetera of as. And there comes my question: which meanings of these, as and to, make such meaning, about, in the sentence above? How do they "converge" into such meaning?
Could you give me two sentences that have as or to whose meaning is used to make the meaning - One sentence that has as whose meaning of above, and another sentence that has to whose meaning of above.