A user cannot access the cron scheduling system. What file needs to be modified to provide that access?

(Specify full path and filename)

Answer: /etc/cron.allow

Explanation:
From the man pages:
If the /etc/cron.allow file exists, then you must be listed therein in order to be allowed to use this command. If the /etc/cron.allow file does not exist but the /etc/cron.deny file does exist, then you must not be listed in the /etc/cron.deny file in order to use this command.