This command will remove all containers, regardless of their state, by passing the IDs of all containers to the docker rm command. The docker ps -aq command will list the IDs of all containers, including the ones in an exited state, and the $ ( ) syntax will substitute the output of the command as an argument for the docker rm command. This is a quick and easy way to clean up all containers, but it may also remove containers that are still needed or running.
References
* docker rm | Docker Docs - Docker Documentation, section "Remove all containers"
* Docker Remove Exited Containers | Easy methods. - Bobcares, section "For removing all exited containers"

To enable LUKS on a USB storage device with an ext4 filesystem format, the administrator needs to perform the following steps:
* Unmount the device if it is mounted using umount /dev/sdc (D)
* Create a partition table on the device using fdisk /dev/sdc (E)
* Format the partition with LUKS encryption using cryptsetup luksFormat /dev/sdc1 (H)
* Open the encrypted partition using cryptsetup luksOpen /dev/sdc1 LUKS0001
* Create an ext4 filesystem on the encrypted partition using mkfs.ext4 /dev/mapper/LUKS0001
* Mount the encrypted partition using mount /dev/mapper/LUKS0001 /mnt References:
* [CompTIA Linux+ Study Guide], Chapter 9: Securing Linux, Section: Encrypting Disks
* [How to Encrypt USB Drive on Ubuntu 18.04]

Terraform is a tool for building, changing, and managing infrastructure as code in a cloud-based environment.
Terraform uses configuration files to describe the desired state of the infrastructure and applies changes accordingly. Terraform supports various cloud providers, such as AWS, Azure, Google Cloud Platform, and more.
To validate changes before they are applied to the cloud-based environment, the administrator can use the terraform plan command. This command will compare the current state of the infrastructure with the desired state defined in the configuration files and show what actions will be performed to achieve the desired state. This command will not make any changes to the infrastructure but only show a plan of changes. The statement D is correct.
The statements A, B, and C are incorrect because they do not validate changes before they are applied to the cloud-based environment. Ansible is another tool for automating infrastructure management, but it does not have a plan command. Git clone and git pull are commands for working with git repositories, which are used for version control of code. References: [How to Use Terraform to Manage Cloud Infrastructure]