[Ans: A]

When a client tries to access a protected resources without authenticating, the server will send a 401 Unauthorized message back to the client. The response message includes a header that tells the client browser that Basic Authentication is needed to access the resource.

The following is a sample response sent by a server:

HTTP /1.0 401 Unauthorized
Server: Tomcat/4.2
WWW-Authenticate: Basic realm="finance"