单项选择题 A network printer will not print. The printer is online and visible. All the print jobs complete but the printer will not operate. Which of the following is the MOST likely cause?（）

单项选择题 The local library has several public desktops and is concerned about PCs being opened andcomponents being stolen. Which of the following could prevent this?（）

单项选择题 A user states that all their incoming mail is showing that it is behind three hours. All other users have the correct time. Which of the following should the technician check?（）