Identify the logical structure that will never have more than one data segment created for it.（）

A.Each segment contains one or more extents.
B.Multiple tablespaces can share a single data file.
C.A data block is the smallest unit of input/output （I/O） in data files.
D.It is possible to have tablespaces of different block sizes in a database.
E.Each data block in the database always corresponds to one operating system block.

A.System monitor （SMON）
B.Process monitor （PMON）
C.Memory manager process （MMAN）
D.Manageability Monitor process （MMON）

A.It is possible to have multiple database writers in an Oracle instance.
B.It writes dirty buffers， if any， to data files whenever a checkpoint occurs.
C.It writes dirty buffers， if any， to data files whenever a transaction commits.
D.It writes dirty buffers， if any， to data files before the log writer （LGWR） writes.