What does the entry valid users = @smbusers in the smb.conf file mean when used in a share section?

A.
Only users connecting from the machine called smbusers can use this share.

B.
Files saved in the specified share will be owned by the group smbusers.

C.
Only users in the unix group called smbusers can access this share.

D.
Only the user account smbusers can access this share.