Which command is used to initialize a working directory containing Terraform configuration files?

The command used to initialize a working directory containing Terraform configuration files is "terraform init." This command prepares the directory for other Terraform commands by setting up the necessary file structures, downloading provider plugins, and verifying that the required plugins are available.

When you run "terraform init," Terraform performs several critical tasks:

1. Provider Initialization: It detects which providers are specified in the configuration files and downloads the required provider binaries from the Terraform Registry. This ensures that you have the correct version of each provider necessary for your project.

2. Backend Initialization: If you are using a remote backend for storing your Terraform state, "terraform init" will configure it as specified in your configuration files. This enables the management of your state file remotely.

3. Module Installation: If your configuration references any modules, "terraform init" will also retrieve those modules, ensuring that your configuration will function as intended.

4. File Structure Setup: It sets up the necessary folder structures and files to ensure the working directory is ready for further Terraform commands.

The other choices do not serve this purpose. "terraform start," "terraform bootstrap," and "terraform configure" are not valid Terraform commands, as they do not perform the initialization functions that "terraform init