We don’t know if ‘theirs’ applies to a single car they own or if they both own a car (assuming just two people), because we don’t know the context. So, I’d have thought that ‘les leurs’ is as legitimate an answer as ‘la leur’.
I do apologise for the long delay in replying to your query.
I think the example you are referring to is the following: "I like my car. I like theirs too.)"
It is correct that without any other context, both (la leur / les leurs) should be accepted. They are now both marked as correct options.
Merci de votre contribution !
Bonne journée !
Sign in to submit your answer
Don't have an account yet? Join today
Test your French to the CEFR standard