Don’t turn off the computer before closing all programsyou could have problemsA. orB. andC

Don’t turn off the computer before closing all programs you could have problems
A. or
B. and
C. but
D. So

(答案→)A. orB. andC. butD. So解析：根据you could have problems可知，此处是虚拟语气的用法，而选项中只有or和but是和虚拟语气连用的，用法为：有时候，虚拟不是通过if引导的条件句来表示，而是暗含在上下文中。用otherwise、or, even though等表示与上文的情况相反，从而引出虚拟语气。如：I lost your address.Otherwise,I would have visited you long before。有时候，虚拟条件通过but暗示出来。如：He would have given you more help,but he was too busy。Or 和but的区别就是，or前面是事实，后面用虚拟，而but是前面用虚拟，后面是事实。本题中，后面是虚拟的内容，因此选择A，意为，在关闭所有程序之前，不要关闭电脑，否则你会遇到问题的。【考点定位】考察虚拟语气的用法。

这个答案应该是对的