Which control mechanism prevents simultaneous transactions from conflicting in a database?

Concurrency control is the correct choice for preventing simultaneous transactions from conflicting in a database. This mechanism ensures that multiple transactions can occur simultaneously without leading to inconsistencies in the database. It achieves this by coordinating the access that transactions have to shared resources, thus allowing for effective execution without interruptions or conflicts.

In the context of database operations, concurrency control manages how transactions are initiated, executed, and completed while ensuring the ACID properties (Atomicity, Consistency, Isolation, Durability) are maintained. This is crucial in multi-user environments where two or more users or applications may attempt to modify the same data at the same time.

While transaction management refers to the broader process of handling transactions, including aspects like committing and rolling back, concurrency control specifically targets the issues that arise from transactional conflicts. Similarly, isolation mechanisms are a subset of concurrency control techniques that help to manage how transaction effects are seen by other transactions, but do not encompass all the aspects of handling simultaneous access. Lock management, on the other hand, is a technique used within concurrency control to enforce isolation by locking data, yet it is just one method among several strategies. Therefore, concurrency control is the most comprehensive answer when discussing the overall mechanism for preventing conflicts in simultaneous transactions.