把一个轻质的小球靠近用毛皮摩擦过的橡胶棒时，它们相互排斥，则这个小球 [ ]

A．一定不带电

B．一定带负电

C．一定带正电

D．可能不带电

The expected time TE used in the PERT algorithm is calculated using the following equation ______.

A) (a+3m+b)/6
B) (a+4m+b))/6
C) (a+5m+b)/6
D) (a+m+b)/3
Note: A major assumption for all network methods is that activity durations are statistically dependent and where a=most optimistic time, b=most pessimistic time, m=most likely time.