It isn't A, because a calculated response would be well thought out, planned. Juliet's response is one of emotion, not reason. For this same reason, it couldn't be circumspect. She hasn't weighed out the different outcomes and the expected results, coming to a logical conclusion that Romeo should not be shamed because of his actions. It also cannot be disingenuous; she is sincere when she says that she doesn't want Romeo to come to shame, despite the fact that he killed her cousin.
We are now left with either "inexplicable," or unable to be explain or account for, and "precipitate" which means to hurl, throw, or cause abruptly. In the context, precipitate appears to be the best choice. Juliet was criticizing and condemning Romeo, but abruptly changes her opinion when the Nurse joins in, calling shame on his head. The remark, "blistered be thy tongue," reads best like a snapped remark, or an insult hurled at the nurse.