Final answer:
The correct verb form to fill in the blank is 'Va'.
Step-by-step explanation:
The correct answer is C. Va. In the dialogue, Marta is being asked where she is going now. The verb form that matches with the subject 'Marta' is 'Va', which means 'he/she goes' in Spanish. So, the correct answer is option C.
Learn more about Verb Forms in Spanish