题干
（2015•广东佛山）Meals are very boring. He ________ has the same thing to eat every day.
A：never
B：usually
C：sometimes
答案(点此获取答案解析）
B
（2015•广东佛山）Meals are very boring. He ________ has the same thing to eat every day.
A：never
B：usually
C：sometimes
为定值电阻，
、
为可调电阻，用绝缘细线将质量为
、带正电的小球悬于电容器内部。闭合电键S，小球静止时受到悬线的拉力为F。调节
