如图所示，沿直径方向开有一凹槽的圆盘水平放置，可绕过中心O点的竖直轴转动，凹槽内有一根轻质弹簧，弹簧一端固定在O点，另一端连接质量为m的小滑块．弹簧的劲度系数为k、原长为l₀，圆盘半径为3l₀，槽底与小滑块间的动摩擦因数μ= $\frac{3k{l}_0}{5mg}$ ，凹槽侧面光滑．圆盘开始转动时，弹簧处于原长l₀．已知重力加速度为g，最大静摩擦力等于滑动摩擦力，弹簧始终在弹性限度内，则在圆盘转动过程中：

$\frac{8}{9}$  减去 $\frac{1}{6}$  与 $\frac{1}{4}$  的和，差是____。

三年级同学要进行团体操表演，老师将180人平均分成2队，每队平均分成3组。每组有多少人?

    Sally is a good girl. She never ____  up late. Her mother wakes her up（唤醒）at 6:00 a.m. From a quarter ____  six, she begins to do sports. The she comes back and has ____  at six forty. After that, she goes to school. Sometimes she ____ her bike.
At school, Sally has seven classes on ____ . Sally is good at（擅长）English. She san speak English very well. After school she often plays ____  games with her ____ . Then she goes home by bus. She gets home before 6:00 p.m.. After
____  she begins to do her ____ . Then she ____  TV for a while, she always goes to bed before half past ten.