Explanation
The best command to use to prevent the httpd web service from being started both manually and automatically on a server is A. systemctl mask httpd. This command will create a symbolic link from the httpd service unit file to /dev/null, which will make the service impossible to start or enable. This is different from systemctl disable httpd, which will only prevent the service from starting automatically on boot, but not manually. The other commands are either not relevant or not sufficient for this task. For example:
C: systemctl stop httpd will only stop the service if it is currently running, but it will not prevent it from being started again.
D: systemctl reload httpd will only reload the configuration files of the service, but it will not stop or disable it.