A:H2SO4
B:HNO3
C:HF
D:H2SiO3
Children to watch thrillers. They may have a bad influence on children.
“文化大革命”结束的标志是( )
有A、B、C三个带电小球,如果小球A带正电,小球C吸引小球B,小球B排斥小球A,那么小球B带____电;小球C带____电.(填“正”或“负”).