Final answer:
Deadlock prevention uses policies to ensure that one of the necessary conditions for deadlocks does not occur, thus preventing the deadlock from happening.
Step-by-step explanation:
The approach that uses a policy to ensure that one of four conditions cannot arise in a system is known as (a) Deadlock prevention. Deadlock prevention is a set of methods for ensuring that at least one of the necessary conditions for a deadlock (mutual exclusion, hold and wait, no preemption, and circular wait) does not occur and thereby preventing the deadlock before it can happen. This is in contrast to deadlock avoidance, which requires additional information about the process states and resources to ensure the system will never enter an unsafe state that could lead to a deadlock. Deadlock detection, on the other hand, is about identifying deadlocks after they occur, and deadlock resolution involves breaking the deadlock once it is detected. Hence, deadlock prevention focuses on structural measures to make deadlocks theoretically impossible by violating at least one of the necessary conditions