A. User jack can use cat to output the contents of testfile because he has read permission as the file owner.

B. User jack can change permissions for testfile because he has execute permission for the file.

C. User jill can edit testfile because she has read and write permission at the group level.

D. User jack can edit testfile because he has read and write permissions at the group level.

E. User jill can change the permissions of testfile because she has write permission for the file at the group level.

F. User jack can change permissions for testfile because he is the owner of the file.