Final answer:
SNMP version 3 includes improvements in agent and manager authentication and SNMP message encryption.
Step-by-step explanation:
SNMP version 3 includes improvements in agent and manager authentication (option c) and SNMP message encryption (option d).
Agent and manager authentication enhances the security of SNMP by verifying the identities of both the agent (the network device being monitored) and the manager (the system managing the SNMP data).
SNMP message encryption adds an extra layer of security by encrypting SNMP messages, preventing unauthorized access to sensitive data transmitted through the network.