________is the reactive modification of a software product performed after delivery, to correct any discovered problems, such as bugs and logical errors.
A. Corrective maintenance
B. Adaptive maintenance
C. Perfective maintenance
D. Preventive maintenance
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This sort of maintenance ________ only about 5% of all maintenance.
A. accounts for
B. counts for
C. accounts up to
D. counts up to
The famous Chinese saying “___________” tells us that we need to maintain the software before there is really something wrong with it.
A. catching the ball before the bound
B. when it rains, it pours
C. saving up before a rainy day
D. pouring oil on troubled waters
达到静平衡的刚性回转件，其质心 位于回转轴线上。
A．一定；
B．不一定；
C．一定不。
D无法确定
转子的许用不平衡量可用质径积[mr]和偏心距[e]两种表示方法，前者 。
A．便于比较平衡的检测精度；
B．与转子质量无关；
C．便于平衡操作。
D.与转子有关
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