Distribution of secret keys to communicating parties

Question

Specify the ways through which the secret keys may be distributed to the two communicating parties.

Answer 1

a) A can selects the key and physically deliver it to the B.

b) A third party may select the key and then physically deliver it to A and B.

c)  If A and B have previously and currently used the key, one party may send the new key to another, encrypted by using the old key.

d) If A and B each has the encrypted connection to the third party C, C may deliver the key upon the encrypted links to A and B.