When is the connection concentrator enabled?（） A: When the value of MAX_CONNECTIONS is greater than the value of MAX_COORDAGENT B:    C: When the value of MAX_AGENTS is greater than the value of MAX_CLIENT D:    E: When the value of NUM_AGENTS is greater than the value of MAX_AGENT F:   G: When the value of NUM_CONNECTIONS is greater than the value of NUM_COORDAGENT H: