[单选题]41、 When deploying an advanced authentication scheme that requires each user at the remote site to enter authentication parameters before tunnel access is granted, which option would you choose for your deployment?当配置一个高级的验证机制时，它需要位于远程站点的每一个用户在隧道访问被准许之前先输入验证参数，你可以选择下面的哪一个选项来进行配置?
A. SUA
B. Unit Authentication 单元验证
C. IUA
D. X-Auth