When the interrogative pronoun replaces the noun and its position does not
change, use quoi as opposed to que.
Use que as opposed to quoi when the pronoun has been moved
to the front of the sentence unless a preposition comes before it.
When que is the subject of a sentence, est-ce qui must be
appended to it- qu'est-ce qui. When an object, continue to attach est-ce
que.
The same is true for qui- when it is the subject of a sentence attach
est-ce qui and continue to attatch est-ce que when an object.