What happens if the password of a user in the /etc/shadow file is prepended with the ! character?

[answerhappygod]

What happens if the password of a user in the /etc/shadow file is prepended with the ! character?

A. When logging in, the user automatically gets root privileges in addition to his regular privileges.
B. The password is inverted which allows the user to log in with any password other than the current password.
C. The user is disabled and all login methods, including but not limited to password based logins, are disabled.
D. Upon the next log in, the user is forced to change his password.
E. The password becomes invalid which disables password based logins although other login methods remain usable.