[单选题]
A Styrofoam ball of mass 0.120 g is placed in an elem( 3 xsr6x.(ltl rwtxy ;*-exictric field of 6000 N/C wsld v.lb7 5rm 54sx;b+,s8lw,gxyfvpointing downward. What charge must be plm g4,7srlxx+d;lb,wsbfw y.5l v8v5s aced on the ball for it to be suspended?
