Which is the BEST choice to indicate a preventive control?

Preventive controls are security measures that are designed to prevent a security incident from happening in the first place. Data backups are a preventive control because they help to protect data from being lost or corrupted. If a security incident does occur, such as a ransomware attack, the data can be restored from the backups.

The other options are not preventive controls. A door alarm is a detective control, which means it detects a security incident after it has happened. A security camera is also a detective control. Smoke detectors are a mitigative control, which means they help to mitigate the damage caused by a security incident.