质点做直线运动的 v-t 图象如图所示，则由图像可知：        

A．3~4 s 内质点位移为-2 m，加速度为4m/s²

B．4~6 s质点的位移为-4 m，加速度为-2m/s²

C．0 ~4 s 内质点位移为8 m

D．6 s 内质点发生的路程为12m

You are taking over a project and determine the following：Activity B has an early finish(EF)of day 3，a late finish(LF)of day 6，and an early start(ES)of day 2．Activity L is being done by a hard-to-get resource．The cost performance index(CPI) is 1.1 and the schedule performance index(SPI)is 0.8．Based on this information，what would you be more concerned about ？（）

A．Float

B．Resources

C．Cost

D．Schedule