The Black Death is such a large topic that it is easy to imagine going for too broad a focus, and ending up vague. I would therefore take the question in one of two directions, depending on what sort of class this is for.
Possible direction one: How did the Black Death contribute to the emergence of the Renaissance? This question would let you keep a purely historical focus, but would narrow your attention to social and political impacts of the plague.
Possible direction two: How does the Black Death parallel or diverge from other plagues? This would be more open-ended, and could let you explore things like the AIDS epidemic if you liked.