Explanation
The grep command is used to search for a pattern in a file or input. The -i option makes the search case-insensitive, meaning that it will match both uppercase and lowercase letters. The grep command takes the pattern as the first argument and the file name as the second argument. Therefore, the command grep -i linux operating-systems.txt will find all lines in the file operating-systems.txt which contain the term linux, regardless of the case. References: Linux Essentials - Topic 103: Finding Linux Documentation and Linux Essentials - Topic 104: Command Line Basics

Explanation
The correct command to copy the two files ending in .txt to the /tmp/ directory is cp *.txt /tmp/. This command uses the wildcard character * to match any number of characters beforethe .txt extension. Therefore, it will copy both texts 1.txt and texts 2.txt to the destination directory /tmp/. The other options are incorrect because they use different wildcard characters or syntax that do not match the desired files. For example, option A uses ?? to match exactly two characters before the .txt extension, but the files have a space and a number, which are not considered as one character. Option C uses a backslash \ to escape the dot . before the .txt extension, but this is unnecessary and will cause the command to fail. Option D uses ? to match exactly one character before the .txt extension, but the files have more than one character. Option E uses $? to match the exit status of the previous command before the .txt extension, but this is not relevant and will cause the command to fail123 References: 1: Linux wildcards | How do wildcards work in Linux with examples? - EDUCBA 2: Wildcards in Linux explained with 10 examples | FOSS Linux 3: What are wildcard characters in Linux? - Sage-Answers

Explanation
The passwd command in Linux is used to change the password of a user account. A normal user can run passwd to change their own password, and a system administrator (the superuser) can use passwd to change another user's password, or define how that account's password can beused or changed1. The passwd command can also be used to lock or unlock a user account. Locking a user account means disabling the user's ability to log in to the system, while unlocking a user account means restoring the user's ability to log in. To lock a user account, the passwd command can be used with the -l option, followed by the username. To unlock a user account, the passwd command can be used with the -u option, followed by the username12. The passwd command cannot be used to change a user's username, create a new user account, or create a new user group. These tasks require different commands, such as usermod, useradd, orgroupadd345. References: 1:
Linux Passwd Command Help and Examples 2: Passwd command in Linux: 8 Practical Examples 3:
usermod(8) - Linux man page 4: useradd(8) - Linux man page 5: groupadd(8) - Linux man page

Explanation
DHCP stands for Dynamic Host Configuration Protocol. It is a protocol that provides quick, automatic, and central management for the distribution of IP addresses within a network. It also configures other network information, such as the subnet mask, default gateway, and DNS server information, on the device1. DHCP uses a client/server architecture, where a DHCP server issues unique IP addresses and automatically configures the devices that request them2. DHCP allows devices to move freely from one network to another and receive an IP address automatically, which is helpful with mobile devices1.
The other options are not protocols used for automatic IP address configuration. NFS stands for Network File System, which is a protocol that allows a user to access and modify files over a network as if they were on their own computer. LDAP stands for Lightweight Directory Access Protocol, which is a protocol that provides access to a centralized directory service that stores information about users, groups, computers, and other resources on a network. SMTP stands for Simple Mail Transfer Protocol, which is a protocol that enables the sending and receiving of email messages over a network. DNS stands for Domain Name System, which is a protocol that translates domain names into IP addresses and vice versa. References:
* Linux Essentials Exam Objectives, Version 1.6, Topic 105.1, Weight 4
* What Is DHCP? (Dynamic Host Configuration Protocol) - Lifewire
* Dynamic Host Configuration Protocol (DHCP) | Microsoft Learn
* Dynamic Host Configuration Protocol - Wikipedia
* How does AutoIP work? - Barix
* [Network File System - Wikipedia]
* [Lightweight Directory Access Protocol - Wikipedia]
* [Simple Mail Transfer Protocol - Wikipedia]
* [Domain Name System - Wikipedia]

Explanation
The correct command to create an archive file work.tar from the contents of the directory ./work/ is tar
-cf work.tar ./work/. This command uses the -c option to create a new archive, the -f option to specify the file name, and the ./work/ argument to indicate the source directory. The other commands are incorrect for various reasons:
* A. tar --new work.tar ./work/ is incorrect because there is no --new option in the tar command.
The correct option for creating a new archive is --create or -c.
* C. tar -create work.tgz -content ./work/ is incorrect because the -content option is not valid. The correct option for specifying the source files or directories is --files-from or -T. Also, the work.tgz file name implies compression, but the command does not use any compression option such as -z,
-j, or -J.
* D. tar work.tar < ./work/ is incorrect because the tar command does not accept input redirection from the standard input. The correct way to use the tar command is to provide the options and arguments after the command name.
* E. tar work > work.tar is incorrect because the tar command does not produce output redirection to the standard output. The correct way to use the tar command is to use the -f option to specify the output file name. References: : tar command in Linux with examples - GeeksforGeeks : tar Command in Linux With Examples | phoenixNAP KB