The correct answer is B.
OBJ-4.4: The best recommendation is to conduct the elevator control system’s logical or physical isolation from the rest of the production network and the internet. This should be done through the change control process that brings the appropriate stakeholders together to discuss the best way to mitigate the vulnerability to the elevator control system that defines the business impact and risk of the decision. Sudden disconnection of the PLCs from the rest of the network might have disastrous results (i.e., sick and injured trapped in an elevator) if there were resources that the PLCs were dependent on in the rest of the network. Replacement of the elevators may be prohibitively expensive, time-consuming, and likely something that the hospital would not be able to justify to mitigate this vulnerability. Attempting further exploitation of the buffer overflow vulnerability might inadvertently trap somebody in an elevator or cause damage to the elevators themselves.