多项选择题
Which three protocols use UDP as a transport protocol by default?（）
A. HTTP B. TFTP C. DNS D. SNMP E. SMTP
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?（）
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?（）
