单项选择题 Which of the following ports does POP3 services use, by default?（）

单项选择题 A user took a laptop on vacation and made changes to the configuration in order to use the device at the hotel. The user can reach the Internet, but cannot access any internal network resources. Which of the following is the MOST likely reason?（）

单项选择题 A technician is reporting wireless transmission speeds of 300Mbps. Which of the following wireless standards is being used?（）