单项选择题 Which of the following allows verification of the port that a printer is currently using?（）

单项选择题 Which of the following protocols uses port 80?（）

单项选择题 While performing a preventative maintenance check on a personal computer, a technician notices thatseveralunused expansion card slots have open ports. Which of the following BEST describes why the covers for these card slots should be reinstalled?（）