Which option does not keep secret variable values out of Terraform configuration files?

The correct answer is D because marking a Terraform variable as sensitive does not, by itself, keep the value out of Terraform configuration files. The sensitive argument only changes how Terraform displays the value in CLI output, plans, and logs. It does not supply the value from outside the configuration, and it does not prevent sensitive values from being stored in state when those values are used by resources or outputs. Passing values through environment variables, command-line -var arguments, or secure external credential files can help avoid hardcoding secrets directly in .tf files. In Terraform workflows, sensitive values should be kept out of version-controlled configuration and handled through secure runtime mechanisms such as environment variables, HCP Terraform sensitive variables, or Vault.