[单选题]47、 Your remote users are complaining of loss of quality during their voice calls when connected to the VPN. Which of the following protocols can you use to improve the performance of their applications?你的远程用户正在抱怨，当连入到VPN后，整个通话期间语音质量很差。你可以使用下面哪个协议来提高这些应用程序的性能?
A. TCP
B. TLS
C. DTLS
D. UDP
E. DPD