多项选择题
You have been asked to develop an application that uses only connection-oriented protocols. Which two protocols can you use?（）
A. PPP B. UDP C. TCP D. ICMP
多项选择题 Which two characteristics describe the UDP protocol?（）
多项选择题 Which two statements are true of a network mask?（）
单项选择题 What is the purpose of a network mask?（）
