Inversion is also possible with the so-called open questions, asking for a situation. Here, we have different options: the inversion or the construction with est-ce que.
Examples
Comment
est-il possible, qu' il n' ait plus d'argent?
How is it possible that he has no money anymore?
(Comment est-ce
qu'il est possible, qu'il n'ait plus d'argent?).
Qui as-tu vu là-bas?
Whom have you seen?
(Qui est-ce que tu
as vu là-bas?)
Quand vient-il?
When does he come?
(Quand est-ce qu'il vient?)
Quelle pomme veux-tu?
Which apple do you want?
(Quelle pomme est-ce
que tu veux?)
However, the inversion is not possible, if the question refers to the subject of the sentence.
