The correct answer is C. write.
The write command is used to send a message to another user who is currently logged in. The message will appear in the other user’s terminal as if they had typed it themselves. The other user can then respond to the message, and so on.
The mail command is used to send a message to another user who is not currently logged in. The message will be delivered to the user’s mailbox, and they can read it when they next log in.
The mesg command is used to control whether or not you are allowed to receive messages from other users. If you type mesg n, you will not receive any messages. If you type mesg y, you will receive messages.
The grep command is used to search for text within a file.
E is not the correct answer because it is not a command that can be used to have a two-way communication with any person who is currently logged in.