单项选择题 A technician is trying to retrieve a screw that fell inside a case and is just out of reach. Which of the following is the BEST procedure to retrieve the screw?（）

单项选择题 A technician is troubleshooting a laptop LCD, and when the cover is opened nothing shows on the screen. Then all of a sudden the screen comes on and works fine. Which of the following should the technician check FIRST?（）

单项选择题 Which of the following commands would be used to verify the integrity of critical system files?（）