题干
What does Lily want to do with Dave this evening?
A：To watch the basketball game
B：To play in the park．
C：Tb play basketball．
答案(点此获取答案解析）
A
What does Lily want to do with Dave this evening?
A：To watch the basketball game
B：To play in the park．
C：Tb play basketball．
和+
的相同金属小球（均可视为点电荷），固定在相距为
的两处，它们间库仑力的大小为
。两小球相互接触后将其固定距离变为2r，则两球间库仑力的大小为 （ ）