You are managing an Oracle Database 11g database with ASM storage. The ASM disk group has the COMPATIBLE.ASM attribute set to 11.1.  Which statements are true regarding extent management and allocation units in the ASM disk group？（）

• A、 The au_size disk group attribute determines the size of allocation units in the disk group. 
• B、 The allocation unit size may vary but the extent size is fixed.
• C、 The allocation unit size and extent size are fixed for all the disks in a disk group and cannot be changed.
• D、 Extent management is completely automated.