The correct answer is "Está jugando fútbol." or option C is the only answer that would work.
This is the correct answer because the question is asking "What are THEY playing?" and we know that estamos and somas are the nosotros form- or the we form. And Estás is the Tú or you form. Leaving Está, or the she/he form left! Here's a picture that might help you out! However, you should know, that están is for "they", it is the plural form!