Which two statements are true about listeners?

Which two statements are true about listeners?

A.
Listeners use only the TCP/IP protocol.

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

C.
Multiple database instances can be registered with a single listener,

D.
Listener-related errors can be traced only at the administrative level.

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

Explanation:
http://docs.oracle.com/cd/E11882_01/network.112/e10835/protocoladd.htm#NETRF179