Examine this list of Database structures: 　　-----1.Tablespaces 　

Examine this list of Database structures: 　　-----1.Tablespaces 　　-----2.Data files 　　-----3.Segments 　　-----4.Extents 　　-----5.Oracle data blocks 　　-----6.OS blocks 　　Which three are true regarding these?

A.A segment with multiple extents can have space in different data files.

B.Segments always consist of more than one extent.

C.Extents always consist of Oracle data blocks.

D.A tablespace can have data files on different file systems.

E.A segment with multiple extents can have space in different tablespaces.

F.Tablespaces always contain multiple segments.

G.Oracle database blocks always consist of multiple OS blocks.

正确答案是ADE