What is the problem?

User jack on host solaris attempts to use ssh to log in to host oracle and receives this message:
jack@solaris:~$ ssh oracle
ssh: connect to host oracle port 22: connection refused
What is the problem?

A.
Host oracle does not have a valid host public key.

B.
Host oracle does not have a valid host private key.

C.
Host solaris does not have a valid host public key.

D.
Host does not have a valid host private key.

E.
Host solaris is not configured for host-based authentication.

F.
Host oracle is not configured for host-based authentication.

G.
Host oracle is not running the ssh service.

H.
Host solaris is not running the ssh service.

Explanation:
The host he is trying to connect to (oracle) is not running the required service (ssh).