Answer:
You did not attach the audios.
Step-by-step explanation:
Porque mañana es la prueba: because the test is tomorrow.
Porque no hay clase mañana: because there is not class tomorrow.
Looking at the possible answers offered by the text you have put in, I suppose the person is asked: "Why aren't you doing your homework?" (¿por qué no estás haciendo tu tarea? to be answered: "there is no class tomorrow" (porque no hay clase mañana). Or, "why are you studying today?" (¿por qué estás estudiando hoy?) and answer: "because the test is tomorrow" (Pporque el examen es mañana).
sorry for my answer, but you haven't put the audio and I tried to give you a hand equally, good luck!