Which channel definition will require that client applications using channel ABC establish a mutually authenticated SSL channel?

A.
DEFINE CHANNEL(ABC) CHLTYPE(SVRCONN) + SSLCIPH(NULL_MD5) SSLCAUTH(REQUIRED)

B.
DEFINE CHANNEL(ABC) CHLTYPE(SVRCONN) + SSLCIPH() SSLCAUTH(REQUIRED)

C.
DEFINE CHANNEL(ABC) CHLTYPE(SVRCONN) + SSLCIPH(NULL_MD5) SSLCAUTH(MUTUAL)

D.
DEFINE CHANNEL(ABC) CHLTYPE(SVRCONN) + SSLCIPH() SSLCAUTH(MUTUAL)