This command will create a local port forwarding, which means that connections from the SSH client are forwarded via the SSH server, then to a destination server. In this case, the destination server is the same as the SSH server (localhost), and the destination port is 80. The SSH client will listen on port 8080 on the local machine, and any connection to that port will be forwarded to port 80 on the server. This way, the administrator can securely access the web service running on port 80 on the server by using http://localhost:8080 on the local machine.
The other options are incorrect because:
B) ssh -R 8080:localhost:80 admin@server
This command will create a remote port forwarding, which means that connections from the SSH server are forwarded via the SSH client, then to a destination server. In this case, the destination server is the same as the SSH client (localhost), and the destination port is 80. The SSH server will listen on port 8080 on the remote machine, and any connection to that port will be forwarded to port 80 on the client. This is not what the administrator wants to do.
C) ssh -L 80:localhost:8080 admin@server
This command will also create a local port forwarding, but it will use port 80 on the local machine and port 8080 on the server. This is not what the administrator wants to do, and it may also fail if port 80 is already in use by another service on the local machine.
D) ssh -R admin@server
This command is incomplete and invalid. It does not specify any port numbers or destination addresses for the remote port forwarding. It will also fail if the SSH server does not allow remote port forwarding.
Reference:
CompTIA Linux+ Certification Exam Objectives
How to Set up SSH Tunneling (Port Forwarding)

Explanation
The correct command to list all local accounts in which the UID is greater than 500 is:
awk -F: '$3 > 500 {print $1}' /etc/passwd
This command uses awk to process the /etc/passwd file, which contains information about the local users on the system. The -F: option specifies that the fields are separated by colons. The $3 refers to the third field, which is the UID. The condition $3 > 500 filters out the users whose UID is greater than 500. The action
{print $1} prints the first field, which is the username.
The other commands are incorrect because:
find /etc/passwd -size +500 will search for files that are larger than 500 blocks in size, not users with UID greater than 500.
cut -d: fl / etc/ passwd > 500 will cut the first field of the /etc/passwd file using colon as the delimiter, but it will not filter by UID or print only the usernames. The > 500 part will redirect the output to a file named 500, not compare with the UID.
sed '/UID/' /etc/passwd < 500 will use sed to edit the /etc/passwd file and replace any line that contains UID with 500, not list the users with UID greater than 500. The < 500 part will redirect the input from a file named 500, not compare with the UID.
References:
Linux List All Users In The System Command - nixCraft, section "List all users in Linux using
/etc/passwd file".
Unix script getting users with UID bigger than 500 - Stack Overflow, section "Using awk".

Explanation
The best command to use to transfer the local file accounts.pdf to the remote /tmp directory of the server with the IP address 10.10.10.80 is B. scp accounts.pdf [email protected]:/tmp. This command will use the secure copy protocol (scp) to copy the file from the local machine to the remote server over SSH. The command requires the username and password of the user on the remote server, as well as the full path of the destination directory.
The other commands are either incorrect or not suitable for this task. For example:
A: rsync [email protected]:/tmp accounts.pdf will try to use the rsync command to synchronize files between the local and remote machines, but it has the wrong syntax and order of arguments. The source should come before the destination, and a colon (:) should separate the remote host and path.
C: cp [email protected]:/tmp accounts.pdf will try to use the cp command to copy files, but it does not work over SSH and it has the wrong syntax and order of arguments. The source should come before the destination, and a colon (:) should separate the remote host and path.
D: ssh accounts.pdf [email protected]:/tmp will try to use the ssh command to log into the remote server, but it has the wrong syntax and arguments. The username should come before the remote host, and a file name is not a valid argument for ssh.