Final answer:
The necessary step before files on a computer can be accessed by other devices on a network is turning on file sharing.
Step-by-step explanation:
The answer to the question is A) Sharing. Before any files on your computer can be accessed by other devices on a network, file sharing has to be turned on. This is crucial as it allows other users with the correct permissions to access files from the host machine over a network. However, it is important to enable file sharing carefully to protect sensitive information and avoid unauthorized access.