Disk encryption is the best method for securing a workstation used in financial transactions, such as point-of- sale systems. It ensures that if the workstation is stolen, all data on the disk is encrypted and cannot be accessed without proper credentials. File encryption (B) only encrypts individual files, and USB drive encryption (C) only applies to removable storage. Data-in-transit encryption (A) is not relevant for physical security. Reference: Core 2, Domain 2.6 - Security configurations.