The Terraform collection type that should be used to store key/value pairs is map. A map is a collection of values that are accessed by arbitrary labels, called keys. The keys and values can be of any type, but the keys must be unique within a map. For example, var = { key1 = "value1", key2 = "value2" } is a map with two key/value pairs. Maps are useful for grouping related values together, such as configuration options or metadata. Reference = [Collection Types], [Map Type Constraints]

When you use a remote backend that needs authentication, HashiCorp recommends that you:

Explanation
Option C is the correct way to configure multiple providers in a Terraform configuration. Each provider block must have a name attribute that specifies which provider it configures2. The other options are either missing the name attribute or using an invalid syntax.

Explanation
The reason why the apply fails after adding a new provider to the configuration and immediately running terraform apply in the CD using the local backend is because Terraform needs to install the necessary plugins first. Terraform providers are plugins that Terraform uses to interact with various cloud services and other APIs. Each provider has a source address that determines where to download it from. When Terraform encounters a new provider in the configuration, it needs to run terraform init first to install the provider plugins in a local directory. Without the plugins, Terraform cannot communicate with the provider and perform the desired actions. References = [Provider Requirements], [Provider Installation]

The terraform import command is not part of any other Terraform workflow. It must be explicitly invoked by the user with the appropriate arguments, such as the resource address and the ID of the existing infrastructure to import. Reference = [Importing Infrastructure]