单选题 A manufacturing project has a schedule performance index(SPI)of 0.89 and a cost performance index(CPI)of 0.91．Generally，what is the BEST explanation for why this occurred?
A) The scope was changed．
B) A supplier went out of business and a new one needed to be found．
C) Additional equipment needed to be purchased．
D) A critical path activity took longer and needed more labor hours to complete．

【正确答案】 D
【答案解析】[解析] 某个制造项目的进度绩效指数(SPI)是0.89；成本绩效指数(CPI)是0.91。一般而言，对这种情况出现的最好的解释是?
A) 范围变更。
B) 供应商歇业，需要找新的。
C) 额外的设备需要采购。
D) 关键路径的活动太长，需要更多劳动力时间来完成。
当SPI和CPI比较接近时，可能是由一个原因引起的——投入资源不足。