what is true abount the default behaviour of the ACL mask for the file?

When adding additional users to a file’s extended ACL’s, what is true abount the default behaviour of the ACL mask for the file?

A.
The mask is modified to be run union of all permissions of the file owner, owning group and all named user and groups

B.
The mask is left unchanged

C.
if required, a warning is printed indicating that the mask is too restrictive for the permission being granted

D.
The mask is modified to be the union of all permissions of the owning group and all named users and groups