The command chmod 755 filename.log should be used to set filename.log permissions to -rwxr--r--.
The chmod command is a tool for changing file permissions on Linux file systems. The permissions can be specified in octal notation, where each digit represents the permissions for the owner, group, and others respectively. The permissions are encoded as follows:
* 0: no permission
* 1: execute permission
* 2: write permission
* 4: read permission
* 5: read and execute permissions (4 + 1)
* 6: read and write permissions (4 + 2)
* 7: read, write, and execute permissions (4 + 2 + 1)
The command chmod 755 filename.log will set the permissions to -rwxr--r--, which means that the owner has read, write, and execute permissions (7), the group has read and execute permissions (5), and others have read and execute permissions (5). This is the correct command to use to accomplish the task. The other options are incorrect because they either set the wrong permissions (chmod 640, chmod 740, or chmod 744) or do not exist (chmod -G). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 11:
Managing Files and Directories, page 345.

Explanation
The command that would ensure the server is set to runlevel 5 is systemctl isolate graphical.target. This command will change the current target (or runlevel) of systemd to graphical.target, which is equivalent to runlevel 5 in SysV init systems. Graphical.target means that the system will start with a graphical user interface (GUI) and all services required for it.
The other options are not correct commands for setting the server to runlevel 5. The systemctl isolate multi-user.target command will change the current target to multi-user.target, which is equivalent to runlevel 3 in SysV init systems. Multi-user.target means that the system will start with multiple user logins and networking, but without a GUI. The systemctl isolate network.target command will change the current target to network.target, which is not a real runlevel but a synchronization point for network-related services.
Network.target means that network functionality should be available, but does not specify whether it should be started before or after it. The systemctl isolate basic.target command will change the current target to basic.target, which is also not a real runlevel but a synchronization point for basic system services. Basic.target means that all essential services should be started, but does not specify whether it should be started before or after it. References: systemd System and Service Manager; systemd.special(7) - Linux manual page

The command visudo -c can be used to check the validity of the sudo rules in the /etc/sudoers file.
The visudo command is a tool for editing and validating the /etc/sudoers file, which defines the rules for the sudo command. The -c option checks the syntax and logic of the file and reports any errors or warnings. The command visudo -c will verify the sudo rules and help the administrator avoid any mistakes. This is the correct command to use for this task. The other options are incorrect because they either do not check the validity of the file (test, sudo, or cat) or do not exist (sudo vi check). References: CompTIA Linux+ (XK0-
005) Certification Study Guide, Chapter 18: Securing Linux Systems, page 546.

When echoing something to a file, >> appends to the file and > overwrites the file.

The /boot/efi directory is the mount point in a UEFI system. This directory contains the EFI System Partition (ESP), which stores boot loaders and other files required by UEFI firmware. The /sys/efi directory does not exist by default in Linux systems. The /efi directory does not exist by default in Linux systems. The /etc/efi directory does not exist by default in Linux systems. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 11: Managing the Linux Boot Process, page 398.