Every possible means to prevent the crash , but the computer doesn’t still workA. is use

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A. is used
B. are used
(答案→)C. has been used
D. have been used
解析：考察used用法。Be used to 习惯于某事：被用来做某事；used to do sth过去常常做某事。句意：每一种可能的方法都被用来预防崩溃，但是电脑仍旧不能运行。可知描述的是现在已完成的动作，故用现在完成时态。主语means为不可数名词，不可数故助动词用has，选D。