如图所示，杠杆在力F₁、F₂作用下处于平衡状态，L₁为F₁的力臂。请在图中作出F₂的力臂L₂及力F₁.

成年人全身血液总量正常约占体重的____ %，一次失血超过____ 毫升就会发生生命危险．

阅读下文，回答问题

    ①那是一个老师告诉我的故事，至今仍珍藏在心里，让自己明白在人世间，其实不应该放过每一个能够帮助别人的机会。

    ②多年前的一天，这位老师正在家里睡午觉，突然，电话铃响了，她接过来一听，里面却传来一个陌生粗暴的声音：“你家的小孩偷书，现在被我们抓住了，你快来啊！”在话筒里传来一个小女孩的哭闹声和旁边人的呵斥声。她回头看着正在看电视的唯一的女儿，心中立即就明白过来是怎么回事了。

    ③她当然可以放下电话不理，甚至也可以斥责对方，因为这件事和她没任何关系。

    ④但自己是老师，说不定她就是自己的学生呢？此时此刻，那个一念之差的小女孩，一定非常惊慌害怕，正面临着尴尬的境地。犹豫了片刻之后，她问清了书店的地址，匆匆忙忙赶了过去。正如她预料的那样，在书店里站着一位满面泪痕的小女孩，而旁边的大人们，正恶狠狠地大声斥责着。她一下子（走、冲）上去，将那个可怜的小女孩（搂、拉）在怀里，转身对旁边的售货员（严厉、严肃）地说：“有什么事就跟我说吧，我是她妈妈，不要吓着孩子。”在售货员不情愿的嘀咕声中，她交清了28元的罚款，才领着这个小女孩走出了书店，并看清了那张被泪水和恐惧弄得一塌糊涂的脸。

    ⑤她笑了起来，将小女孩领到家中，好好清理了一下，什么都没有问，就让小女孩离开了。临走时，惊魂未定的小女孩，深深地看了她一眼，便飞一般地跑掉了。

    ⑥时间如流水匆匆而过，不知不觉间，多少年的光阴一晃而过，她早已忘了这件事，依旧住在那里，过着平稳安详的生活。

    ⑦有一天中午，门外响起了一阵敲门声。当她打开房门后，看到了一位年轻漂亮的陌生女孩，露着满脸的笑容，手里还拎着一大堆礼物。“你找谁？”她疑惑地问着，但女孩却激动地说出了一大堆话。好不容易，她才从那陌生女孩的叙述中恍然明白，原来，她就是当年那个偷书的小女孩，刚从某名牌大学毕业，已找到了一份令人羡慕的工作，现在特意来看望自己。女弦眼睛泛着泪光，激动地说：“___________________________________________________________________________

____________________________________________________________________________________。”

⑧望着女孩脸上幸福的笑容，她也笑了。

    We often hear stories of animals rescuing people .But now someone has managed to return the favor .

    The event took place one snowy January morning Thomas Smith was walking his dog, Jack, in the park." As I was walking, I just saw Jack running onto the ice towards the ducks in the middle, and then he fell into the water and couldn't climb out, "said Smith.  He realized he had no choice but to try and save his dog." someone else told me the lake was only one - meter deep, but it was at least twice that. I had to break my way through the 6- cm ice. Finally, I got Jack by the neck, and pulled him out. I don't think I have ever felt so cold by the time we got back to dry land. And when we got there, everyone was asking if Jack was okay------ no one was particularly worried, about me!"

    A neighbor, Julie Brown, saw it all happen."The dog went onto an icy lake. All of a sudden, it started to go under. There were crowds of people around, and they were all shouting and screaming. Before I knew it, the owner Smith was in the water forcing his way through the ice. I can't begin to imagine how cold it was. Everyone was very nervous, but he was as cool as a cucumber — he just crawled back out, put the dog on its lead, and went home."

    Many regard him as a hero, but Mr. Smith is quite laid- back about it."Most dog owners are the same as me.They would do what I did without a second thought. But in the future, I'm going to make sure he's on lead near any ice ponds,

    Pets are members of our family. Would you do the same for them?