用括号内所给词的适当形式填空。

1. My _____ (parent) are at home.

2. I like eating _____ (they).

3. _____ (her) is my sister Gina.

4. She is my _____ (mother) friend.

5. Thanks for_____ (help) me.

6. This is _____ (you) class.

在水平转台上有一两端固定的水平横杆，杆上套一质量为m的小球（可视作质点）。球可沿杆无摩擦地滑动，现用两根劲度系数均为K的轻弹簧（也套在横杆上）将小球拴住，横杆与轴O在同一竖直平面内，轴O位于水平转台的中央，转台静止时两根弹簧均未有形变，小球所在点P轴O的距离为L，如图所示，转台以角速度ω绕竖直轴O旋转时，小球移到了另一点P′，与横杆保持相对静止，这时P′与P点之间的距离△L＝？