Turning a sentence into a question

Question

The test asked non specifically to turn "Elles sont parties avant la fin du film" into a question. While I know that I can reverse the order of the subject and the conjugated verb, isn't it also ok to use the phrase "est-ce qu' "?
My response "Est-ce qu'elles sont parties avant la fin du film" was marked incorrect and I am unclear why

Accepted Answer

Bonjour Kay,
You can ask a question in Le Passé Composé using "Est-ce que + statement" in Le Passé Composé or by inverting the auxiliary with the subject, as per the lesson content of the link in your question:

Est-ce que tu as mangé ton petit-déjeuner ? = Have you eaten your breakfast yet?
As-tu mangé ton petit-déjeuner ? = Did you eat your breakfast?

Attention:

Quand as-tu mangé ? = When did you eat?
Comment as-tu mangé ? = How did you eat?
Où as-tu mangé ? = Where did you eat?

I hope this is helpful.
Bonne journée !

Answer

From the link in your question I deduce that the lesson was about forming inverted questions. Does that give you a clue? ;)