Dramatic irony means that the audience knows something the characters do not. For example, in the beginning of Hamlet, we know immediately that Claudius was the one who killed Hamlet's father, however, he doesn't know that from the very start.
So, Dr. Faustus is an embodiment of curiosity gone wild. His blase attitude towards humanistic science is, however, some kind of a scientific decadence: he casts away philosophy and law, to embrace magic, as a relic of medieval obsession over mysticism. In this regard, he is a subversion of the Renaissance Man. He thinks he has already learned all there was to learn about this world, so now he yearns for another kind of knowledge - esoteric, otherworldly, knowledge that isn't exactly a knowledge because you don't have to study long and hard for it, you just have to sell your soul to Lucifer.
C is the answer. Because deleterious is the opposite of helpful. And ominous is the opposite of friendly.
