The correct answer is: A. /etc/ftpusers
The file /etc/ftpusers contains a list of users who are not allowed to access a system via FTP. The file is formatted as a list of usernames, one per line. If a user’s name is listed in this file, they will not be able to connect to the FTP server.
The file /etc/hosts.deny is used to control access to a system via TCP/IP. It contains a list of hosts that are not allowed to connect to the system. The file is formatted as a list of IP addresses, one per line. If a host’s IP address is listed in this file, it will not be able to connect to the system.
The file /etc/ftpaccess is used to control access to an FTP server. It contains a variety of directives that can be used to control who can access the server, what they can do, and how they can do it. The file is formatted as a series of directives, one per line. Each directive has a name and a value. The name specifies what the directive does, and the value specifies how it should be done.
In conclusion, the correct answer is: A. /etc/ftpusers.