Which three statements are true concerning logical and physical database structures? (Choose three.)

A. A segment’s blocks can be of different sizes

B. A smallfile tablespace might be bigger than a bigfile tablespace

C. A segment might have only one extent

D. The extents of a segment must always reside in the same datafile

E. A segment can span multiple data files in some tablespaces

F. Segments can span multiple tablespsaces

G. All tablespaces may have one or more data files