Which three statements are true regarding the logical structure of the Oracle database?

Which three statements are true regarding the logical structure of the Oracle database? (Choose three.)

A.
A data block is the smallest unit of I/O for data files.

B.
Each segment contains one or more extents.

C.
Multiple tablespaces can share single data file.

D.
Each data block in the database always corresponds to one OS block.

E.
It is possible to have tablespaces of different block sizes in a database.