单项选择题A.完善性维护 B.适应性维护 C.预防性维护 D.改正性维护
单项选择题A.income=(799,1500,1999,2001) B.income=(799,1501,2000,2001) C.income=(800,1500,2000,2001) D.income=(800,1499,2000,2001)