题目内容：
The earned value technique is a commonly used method of performance measurement. It integrates project scope, cost, and schedule measures to help the project management team assess project performance. If a project’s Schedule Performance Index（SPI=EV/PV） value less than1.0, it means that_（）.
A.the project is a head of its planned schedule
B.less work was completed than was planned
C.the cost overrun for work completed
D.the cost under-run of performance to date
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