Where are user specific crontabs stored?

A.
In the database file /etc/crontab.db which is shared by all users.

B.
As individual per-user files within /var/spool/cron.

C.
As individual per-user files in /etc/cron.user.d.

D.
In the .crontab file in the user’s home directory.

E.
In the file /var/cron/user-crontab which is shared by all users.