Answer:
C. Emma speaks English correctly even though her parents do not speak a word that is not Hungarian.
Step-by-step explanation:
This sentence contains two independent clauses, but the phrase her parents do not speak a word that is not hungarian, is missing a direct object, making the sentence overall, grammatically incorrect. By adding a comma into this example sentence, would either indicate the beginning of a listing, or a separation between two independant clauses, with a direct object.