To answer this question, the user needs to know about Transient Data Queues (TDQs) and how to prevent multiple users from accessing the same TDQ at the same time.

Option A: By issuing an EXEC CICS ENQ against the resource. This option is correct because an ENQ command is used to obtain a lock on a resource, such as a TDQ, to prevent other transactions from accessing it simultaneously. By issuing an ENQ command against the TDQ, a lock is obtained, and other transactions are blocked from accessing the same TDQ until the lock is released with a DEQ command.

Option B: By issuing an EXEC CICS EQN against the resource. This option is incorrect because there is no such command as EQN in CICS.

Option C: By issuing an EXEC CICS DEQ against the resource. This option is partially correct because a DEQ command is used to release a lock on a resource, such as a TDQ, after it has been obtained with an ENQ command. However, it does not prevent multiple users from accessing the same TDQ at the same time.

Option D: By issuing an EXEC CICS DQE against the resource. This option is incorrect because there is no such command as DQE in CICS.

Option E: By issuing an EXEC CICS TDQ against the resource. This option is incorrect because a TDQ command is used to read from or write to a TDQ, but it does not prevent multiple users from accessing the same TDQ at the same time.

Therefore, the correct answer is:

The Answer is: A. By issuing an EXEC CICS ENQ against the resource.