Which two statements are true regarding listeners?

Which two statements are true regarding listeners? (Choose two.)

A.
Listeners use only the TCP/IP protocol.

B.
The listener-related errors can be traced only at the administrative level.

C.
Multiple listener processes can run simultaneously on a host.

D.
Multiple database instances can be registered with a single listener.

E.
Only one database instance can be registered with a single listener at any time.