Answer:
The question that best completes the conversation is:
Milta: ¿Cuál es la fecha del examen?
Explanation:
There are two possible questions that applies in this case: When is the date of the exam? Or What is the date of the exam? however, in the first question, this would be badly written, because when anybody asks with the word "when", don't need writing or saying the date, in that case, the correct question would be: when is the exam? but for this case, how the question is the date, the correct is asking with the word "what".
