单项选择题 A user has discovered that even though they are using the latest version of the anti-virus software,the computer is still being infected by a virus. Which of the following is the BEST solution for this problem?（）

多项选择题 Operating system files for Windows Vista and Windows XP are located in which of the following?（）(Select TWO).

单项选择题 A user reports the system runs fine for a few minutes and then freezes or locks up. Which of the following is the BEST cause of this issue?（）