[单选题]15、 When deploying a full-tunnel VPN connection that will provide for users running delay-sensitive voice and video applications, which protocol should you use?当配置一个全隧道的VPN连接以提供对延迟敏感的语音和视频应用程序的支持时，应当使用哪一个协议?
A. SSL
B. IKEv2
C. DTLS
D. IKEv1