Why is quand on ouvre les cadeaux ? marked correct?

Question

if I were to read Quand on ouvre les cadeaux I would not expect to have a question mark at the end but a following clause. when I open the presents..... I understand that this perhaps is a very informal spoken form for a question where the question is shown by intonation. BUT in this kwiz it was a written question and not a spoke question. For this reason I feel it not right that not marking this phrase as right gives a nearly correct reponse. Ok it is good to realise that there are different levels of french usage , but where is the indictaion in the written form that it was a question, other that the question mark.

Answer

In French, when either inversion, est-ce que, qui est-ce qui, or qu'est-ce que are omitted, then it becomes a matter of a normal statement with intonation of a question.  In the case cited, it is a written, simple question, hence the question mark is the only clue that it was a question.

J'espère que ma réponse vous aide.

Answer

In French, when either inversion, est-ce que, qui est-ce qui, or qu'est-ce que are omitted, then it becomes a matter of a normal statement with intonation of a question.  In the case cited, it is a written, simple question, hence the question mark is the only clue that it was a question.

J'espère que ma réponse vous aide.