Which of the following aptly describes the Unix file /etc/shadow?

Which of the following aptly describes the Unix file /etc/shadow?

A.
The Unix file/etc/shadow is referenced by login when the /etc/passwd file contains an asterisk in the third field.

B.
The Unix file/etc/shadow is referenced by NIS when the /etc/passwd file contains a line with the first character of ‘+’.

C.
The Unix file/etc/shadow is a place to store encrypted passwords without referencing the /etc/passwd file.

D.
The Unix file/etc/shadow is a read-protected file referenced by login when the /etc/passwd file contains a special character in the second field.