题干
Not only ____interested in a football but ____beginning to care about it.
A：the father is ,his family are
B：.the father is , ishis family
C：is the father ,his family are
D：is the father is ,his family i
答案(点此获取答案解析）
C
的绝缘细线，一端固定在O点，另一端系一带电量为
、质量为
的小球，当沿细线方向加上场强为E的匀强电场后，小球处于平衡状态，如图所示，如果给小球一垂直于细线的初速度
，要使小球围绕O点做圆周运动，
