What is true about a background engine？ （）（Choose two.)

A. It is a server-side PL/SQL procedure.

B. When executing a PL/SQL function activity, it will automatically ping (cache) the PL/SQL code.

C. It executes deferred activities in decreasing order of their Cost property value (activities with higher cost value are processed first).

D. It would fail if another background engine process is started to handle the same type of activities within the same item type.

E. During its single invocation, it processes activities that were stuck, deferred or timed out when the background engine was started.