A system administrator is unable to unmount a file system. Which is the appropriate command to determine who or what is accessing the file system？（）

单项选择题Asystemadministratorwantstoconfigureasystemsothatallnewuserswillbeputintothedatabasegroupbydefault.Howwouldthisbeaccomplished？（）

A.remove all other groups from the system
B.run the command mkuser -default "GROUP=database"
C.change the default group in /usr/lib/security/mkuser.default
D.edit /etc/security/group to move all users to the database stanza

单项选择题Asystemadministratorwouldliketomodifythesystemdefaultusercharacteristicssothateachnewuserwillnowbeassigned（bydefault）thecshshellratherthanthekshshell.Whichofthefollowingactionsshouldbeperformed？（）

A.Run the command chlogin -shell "csh"
B.Run the command mkuser -default "SHELL=csh"
C.Edit /etc/passwd and change all "ksh" entries to "csh"
D.Modify the contents of /usr/lib/security/mkuser.default file