The earned value technique is a commonly used method of performance measurement. It integrates project scope, schedule, and cost measures to help the project management team assess project performance. If a project's Cost Performance Index (CPI=EV/AC)  value less than 1.0, it means that ( )
A. the cost savings for work completed
B. the project is ahead of its planned schedule
C. the cost overrun for work completed
D. less work was completed than was planned