How is the file format of /etc/crontab different from a normal crontab file? (Select TWO correct answers)

A.
The /etc/crontab file can specify a year field.

B.
A normal crontab file must be installed with the crontab command.

C.
A normal crontab file allows for environment variable substitution.

D.
The /etc/crontab file has a user field for commands.