A parent's consent /parents' consent

Are all the sentences correct?

A- "You need a parent's consent to get an abortion." (consent from one parent)

B- "You need your parents' consent to get an abortion." (consent from both parents)

C- "You need a parents' consent to get an abortion." (This one is wrong, in my opinion. The indefinite article can't refer to the noun consent, which is uncountable, right? For the sentence to be correct It would have to be something like a parents' consent form, right? )

Thanks in advance.