题干
Losing weight is no easy task. A lot of people who lost weight gain it back over time and end up back _______ they started.
A：where
B：though
C：since
D：after
答案(点此获取答案解析）
A
的值是（ ）
数为k，小球重力为G，平衡时球在A位置，今用力F将小球向下拉长x至B位置，则此时弹簧的弹力为( )
