Which two statements about the background process of the database writer are true?

Which two statements about the background process of the database writer are true?
(Choose two.)

A.
It writes dirty buffers, if any, to data files whenever a checkpoint occurs.

B.
It writes dirty buffers, if any, to data files whenever a transaction commits.

C.
It is possible to have multiple database writers in an Oracle instance.

D.
It writes dirty buffers, if any, to data files before the log writer (LGWR) writes.