Answer: B. Nosotros
Seeing the question, I guess that the highlighted words are "Mis primos y yo". So this can be replaced with "Nosotros", making the new answer, "Nosotros comemos galletas los viernes", which means in English, "We eat cookies on Friday". But if the highlighted words are, "Mis primos", then the correct answer would be, "Ellos", which in English means, "They and I eat cookies on Friday".
Step-by-step explanation:
Hope this helps =)