The security level of a private key system depends on the number of:

A.
encryption key bits.

B.
messages sent.

C.
keys.

D.
channels used.

Explanation:
The security level of a private key system depends on the number of encryption key bits. The larger the number of bits, the more difficult it would be to understand or determine the algorithm. The security of the message will depend on the encryption key bits used. More than keys by themselves, the algorithm and its complexity make the content more secured. Channels, which could be open or secure, are the mode for sending the message.