Although the stakeholders thought there was enough money in the budget, halfway through the project the cost performance index (CPI) is 0.7. To determine the root cause, several stakeholders audit the project and discover the project cost budget was estimated analogously. Although the activity estimates add up to the project estimate, the stakeholders think something was missing in how the estimate was completed. Which of the following describes what was missing?
A、Estimated costs should be used to measure CPI.
B、SPI should be used, not CPI.
C、Bottom-up estimating should have been used.
D、Past history was not taken into account.