64、维护阶段的关键任务是通过各种必要的维护活动使软件系统持久地满足用户的需要。通常的4种维护活动有:改正性维护,适应性维护,完善性维护,防预性维护。
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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