What is "test data management" in large-scale enterprise testing, and why is it a non-trivial problem?

A Coordinating the creation, masking, refreshing, and isolation of realistic test data across environments, which is difficult due to data privacy regulations, data volume, and dependencies between systems B Simply copying the production database to every developer's laptop with no changes C A concept that applies only to unit tests with no external data D A problem that does not exist if the application has no database