Explanation
The issue is caused by the lack of a default route defined in the /etc/sysconfig/network-scripts/ifcfg-enp0s3 file. A default route is a special route that specifies where to send packets that do not match any other routes in the routing table. Without a default route, the server will not be able to communicate with hosts outside its local network. The default route is usually configured with the GATEWAY option in the network interface configuration file. For example, to set the default gateway to 192.168.1.1, the file should contain:
GATEWAY=192.168.1.1
The other options are not causing the issue. The DNS address is not commented out in the configuration file, it is specified with the DNS1 option. The search entry in the /etc/resolv.conf file is correct, it specifies the domain name to append to unqualified hostnames. Wired connection 1 is online, as indicated by the ONBOOT=yes option and the output of ip link show enp0s3 command. References: Configuring IP Networking with nmcli; Configuring IP Networking with ifcfg Files

Explanation
The command that would resolve the issue is chmod 600 .ssh/authorized_keys. This command will change the permissions of the .ssh/authorized_keys file to 600, which means that only the owner of the file can read and write it. This is necessary for SSH key authentication to work properly, as SSH will refuse to use a key file that is accessible by other users or groups for security reasons. The output of ls -l shows that currently the
.ssh/authorized_keys file has permissions of 664, which means that both the owner and group can read and write it, and others can read it.
The other options are not correct commands for resolving the issue. The restorecon .ssh/authorized_keys command will restore the default SELinux security context for the .ssh/authorized_keys file, but this will not change its permissions or ownership. The ssh_keygen -t rsa -o .ssh/authorized_keys command is invalid because ssh_keygen is not a valid command (the correct command is ssh-keygen), and the -o option is used to specify a new output format for the key file, not the output file name. The chown root:root
.ssh/authorized_keys command will change the owner and group of the .ssh/authorized_keys file to root, but this will not change its permissions or make it accessible by the user who wants to log in with SSH key authentication. References: How to Use Public Key Authentication with SSH; chmod(1) - Linux manual page

Explanation
The administrator should do the following two actions to resolve the issue:
Boot the system on a LiveCD/ISO. This is necessary to access the system and repair the boot loader. A LiveCD/ISO is a bootable media that contains a Linux distribution that can run without installation. The administrator can boot the system from the LiveCD/ISO and mount the root partition of the system to a temporary directory, such as /mnt.
Execute grub-install /dev/sdX and reboot. This will reinstall the GRUB boot loader to the disk device, where sdX is the device name of the disk, such as sda or sdb. The GRUB boot loader is a program that runs when the system is powered on and allows the user to choose which operating system or kernel to boot. The issue is caused by a corrupted or missing GRUB boot loader, which prevents the system from booting. The command grub-install will restore the GRUB boot loader and fix the issue.
The other options are incorrect because they either do not fix the boot loader (interrupt the boot process in the GRUB menu or fix the partition modifying /etc/default/grub) or do not use the correct syntax (grub-install
--root-directory=/mnt instead of grub-install /dev/sdX or rescue or single instead of recovery in the GRUB menu). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 8: Managing the Linux Boot Process, pages 265-266.

Explanation

To create an appropriate device label, format and create an ext4 file system on the new partition, you can use the following commands:
To create a GPT (GUID Partition Table) label on the new drive /dev/sdc, you can use the parted command with the -s option (for script mode), the device name (/dev/sdc), the mklabel command, and the label type (gpt). The command is:
parted -s /dev/sdc mklabel gpt
To create a primary partition of 10 GB on the new drive /dev/sdc, you can use the parted command with the -s option, the device name (/dev/sdc), the mkpart command, the partition type (primary), the file system type (ext4), and the start and end points of the partition (1 and 10G). The command is:
parted -s /dev/sdc mkpart primary ext4 1 10G
To format and create an ext4 file system on the new partition /dev/sdc1, you can use the mkfs command with the file system type (ext4) and the device name (/dev/sdc1). The command is:
mkfs.ext4 /dev/sdc1
You can verify that the new partition and file system have been created by using the lsblk command, which will list all block devices and their properties.