Which statement is correct regarding to user management?

a. In CentOS 8, Only root user can read "/etc/shadow" file.
b. In Windows Server 2019, only one domain controller can be deployed if Active Directory is adopted.
c. In CentOS 8, Each user has one default group, and its default group can be found in "/etc/group".
d. In Windows Server 2019, Active Directory can provide distributed user account management, but cannot be used for computer management.