（2015•哈尔滨）小聪测量了如图所示的滑轮组的机械效率，他先后进行了两次实验，将钩码分别匀速竖直提升h₁和h₂的高度（h₁＞h₂）．对两次实验中一些物理量进行比较，正确的是（其中s为绳子自由端通过的距离，H为动滑轮上升的高度）（　　）

找出文中反复出现“我们手拉手……”的句子，谈谈作用。

    If you have a mobile phone，the Internet could always be with you．And that is often a good thing．You can use the Internet for ____，learning and talking with your Mends．But the Internet can also be a ____place. The good news is that it really isn't too hard to protect (保护) ____．Following these tips will let you enjoy the Internet and keep you safe(安全的)．

    Take control of your personal information．First．don't ____too much online．For example，don't put your phone number or real ____on the Internet．Second，make sure you know who is ____your personal information．Don't let everyone see everything you put on the Internet．

    Be careful of strangers(陌生人)．It can be fun to meet interesting and ____people on the Internet，but be careful．Some children have found themselves in a dangerous situation ____they agreed to meet online friends in real life．

    Use your time online to make the Internet a better place. Don't say things that will ____other people．Don't send rude(粗鲁的) ____．And delete people who are often rude．

根据拼音写出相应的词语。