如图所示，质量均为m的三个带电小球，A、B、C放置在光滑的绝缘水平面上，A与B、B与C相距均为l，A带电Q_A=+8q，B带电Q_B=+q，若在C上加一水平向右的恒力F，能使A、B、C三球始终保持相对静止，则：

（1）外力大小F为多少？

（2）C球所带电量Q_C？

Willpower is a kind of quality, _____ is _____ it takes to do anything well. [ ]

A. what; which

B. what; what

C. which; which

D. which; what