The correct answer is: A. grep
grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. It is one of the most widely used utilities in Unix-like operating systems.
mail is a command-line utility for sending and receiving email messages. It is a simple and easy-to-use tool that can be used to communicate with other users on the same system or on a remote system.
mesg is a command-line utility for managing the user’s message queue. It can be used to send and receive messages from other users on the same system.
write is a command-line utility for sending a message to another user on the same system. It is a simple and easy-to-use tool that can be used to communicate with other users quickly and easily.
Therefore, grep is not a communication command.