The output of the show aaa domain-map displays the following information:Domain: ispcom; virtual-router: vr1; loopback: 1Domain: isp2.com; virtual-router: vr2; loopback: 1Domain: none; virtual-router: vr3; loopback: 1Domain: default; virtual-router: vr4; loopback: 1The 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
参考答案：D
