Tom was a fat boy when he was ten. He liked watching TV very much. He watched TV at least 5 hours every day. Wherever(无论哪里) he went, he would be late.

    One day, he found a pair of special glasses in his post-box(邮箱). He also found a message saying, “With these you can see time.”

    The boy decided to have a try. He put the glasses on, looked at his brother, a tall and thin boy, and saw a big box of flowers on top of his head. And it wasn't just his brother. When he looked at his parents, he also saw the flowers. The three boxes were very large and the flowers were very beautiful. Then, he looked at himself from the mirror. He saw the flowers, too. But his flowers went to the mouth of the television. Its mouth was big. His flowers became fewer and fewer.

    At last, he learned that watching TV was a waste of time. He could learn nothing from it. He decided he would never again let the television eat his time.

一幅图的比例尺是 ，图上的1厘米表示实际距离____千米；实际距离50千米在图上要画____厘米。把这个线段比例尺改写成数值比例尺是____。

在一次救援中，一辆汽车停在一小山坡底，突然司机发现在距坡底240m的山坡处一巨石以8m/s的初速度0.4m/s²的加速度匀加速滚下，巨石到达坡底后速率不变，在水平面的运动可以近似看成加速度大小为0.2m/s²的匀减速直线运动；司机发现险情后经过2s汽车才启动起来，并以0.5m/s²的加速度一直做匀加速直线运动 （如图所示）．求：

据中国青少年犯罪研究会调查，某市2010少年罪犯中，51％的人有了不良行为，家长却不予过问或管不了。在江苏省2008－2010年在押的少年犯中，犯错误后遭父母打的占25•7％。这一材料说明了做好_____________，对青少年避免违法犯罪，健康成长有着重要的作用。（   ）