Alice wants to have an encrypted communication with Bob using key K$.$ Assuming Alice and Bob each has a public and private key pair and they also know each other's public key. To transfer key $K$ securely to Bob, Alice will need to

encrypt $K$ with Alice's public key and send the encrypted $K$ to Bob

encrypt $K$ with Alice's private key and send the encrypted $K$ to Bob

encrypt $K$ with Bob's public key and send the encrypted $K$ to Bob

encrypt $K$ with Bob's private key and send the encrypted $K$ to Bob