The output of the show aaa domain-map displays the following information: Domain: isp1.com; virtual-router: vr1; loopback: 1 Domain: isp2.com; virtual-router: vr2; loopback: 1 Domain: none; virtual-router: vr3; loopback: 1 Domain: default; virtual-router: vr4; loopback: 1 The end user supplies a login name of joe@isp7.com . Which virtual router is responsible for authenticating this user?（）

• A、vr1
• B、vr2
• C、vr3
• D、vr4