I think the point is that returning a car to someone else would be rendu (from rendre), so the only correct answer is "to take it back inside".

I think you're translating a bit too literally in this case. In this sense, Mathilda brought the car back in before it rained seems to be what they're looking for, given the lesson this pertains to.

In your answer, returned could very well mean that she returned the car to someone she borrowed it from, with little context. 

I hope this helps! :)

If you wanted to say that Mathilde returned the car, you would use the verb retourner in French. Rentrer qc. means generally to take something inside.

I thought retourner meant more to "send back" which wouldn't be appropriate for a car. Did you disagree with using rendre?

I guess rendre could work also. I do sense some difference to retourner but I am not sure how to verbalize it. The two verbs haven't acquired enough of a personality for me yet.

For what it’s worth, I keep getting this question wrong. Will re-read the responses. There must be someway to make the explanation stick!