单项选择题
Which of the following DNS record types provides the hostname to IP address mapping?（）
A. A record B. NS record C. CNAME record D. MX record
单项选择题 Which of the following should be updated when new computers are purchased?（）
单项选择题 Which of the following wireless technologies can support the GREATEST distance on either 2.4GHz or 5GHz frequencies?（）
单项选择题 Which of the following protocols can be found at the application layer?（）
