Cost performance measurement is BEST done through which of the following ？（）
A．Asking for a percent complete from each team member and reporting that in the monthly progress report
B．Calculating earned value and using the indexes and other calculations to report past performance and forecast future performance
C．Using the 50/50 rule and making sure the life cycle cost is less than the project cost
D．Focusing on the amount expended last month and what will be expended the following month
