材料一：俄国在其发展的历史上曾遭遇到农奴制和工业化的矛盾…1914年俄国陷入战争泥潭…1917年11月7日，震动世界的革命爆发．

材料二：1920年，三年国内战争结束．苏俄却遇到了巨大困难…人民生活困苦…第二次世界大战中，苏联为世界反法西斯战争做出重要贡献．

材料三：（当时）苏联存在着各种各样的问题…1991年，克里姆林宫的红旗悄然落下，红色的年轮在大国兴起的舞台上刻写了74圈． ﹣﹣摘编自《大国崛起》《世界上下五千年》   

学会自我保护，对未成年人的健康成长至关重要。下列做法正确的是（   ）
①同学溺水，奋不顾身救援    ②公共场所，不忘观察安全出口
③面对歹徒，力求保护自己    ④网络聊天，不轻易泄露个人信息 

Complete the sentences with the given words in their proper forms (用括号中所给单词的适当形式完成下列句子。每空格限填一词)
Climb up to the ____ floor, and you can enjoy a better view. (eleven)
____ , Grace made up her mind to live abroad with her daughter. (final)
It is a very ____ book for language learners to improve writing skills. (use)
Don't worry about your son. He is old enough to be independent and live by ____ . (he)
The movie KungFu Panda II is sure to ____ a large number of teenagers. (attractive)
If you don't go on a diet, it is ____  for you to lose weight. (possible)
The local people had to move away because of the serious ____. (pollute)
The great ____  gave his first show in Shanghai and the tickets sold out in minutes. (art)

观察生活中的物品和儿童玩具，哪些是利用弹性势能工作的？