How can you verify the integrity of the /etc/passwd file?

A.
pwchk

B.
pwck

C.
chkpw

D.
ckpw

Explanation:
From the man pages:
The pwck command verifies the integrity of the users and authentication information. It checks that all entries in /etc/passwd and /etc/shadow have the proper format and contain valid data. The user is prompted to delete entries that are improperly formatted or which have other uncorrectable errors.
Checks are made to verify that each entry has:
the correct number of fields
a unique and valid user name
a valid user and group identifier
a valid primary group
a valid home directory
a valid login shell