During the SIP UA registration process, a response message with a status code of 401 was received, stating that ____?

During the SIP UA registration process, a response message with a status code of 401 was received, stating that ____?
A . UA has been registered on the registration server normally
B . Table showing UA sends a request message packet server sets the field do not know, but it has been ignored server, UA still successfully registered
C . Table shows the server needs UA transmit authentication information, UA after receiving the response, it would Laid own authentication information registration request sent by a second server to register
D . Table shows UA request message sent by the server contains the fields do not know, registration failed

Answer: C