A blocked airway(呼吸道) can kill someone in three to four minutes, but it can take more than eight minutes for an ambulance to arrive. So a simple procedure such as opening someone's airway can save their life while they're waiting for emergency medical help. This means you're more likely to give first aid to someone you know than a stranger.

    There are many misconceptions (误解) surrounding first aid. Below are the ‘most popular' ones with details of what you should do.

    You should put butter or cream on a burn. The only thing you should put on a burn is cold water — keep the butter for cooking. Put the affected area under cold running water for at least ten minutes.

    The best way to treat bleeding is to put the wound under a tap. If you put a bleeding wound under a tap you wash away the body's clotting agents(凝血剂) and make it bleed more. Instead put pressure on the wound with whatever is available to stop or slow down the flow of blood. As soon as possible call 999. Keep pressure on the wound until help arrives.

    Nosebleeds are best treated by putting the head back. If you put the head back during a nosebleed, all the blood goes down the back of the airway. Instead advise them to tilt(倾斜) their head forwards and ask the person to pinch(捏) the end of their nose and breathe through their mouth.

    You need lots of training to do first aid. You don't — what you mostly need is common sense. You can learn enough first aid in a few minutes to save someone's life — whether it's from a book, attending a course or watching videos online.

    Remember: anyone can save a life

阅读材料，完成下列要求。

材料一：洋鬼子怎样就骗了钱去，老通宝不很明白。但他很相信老陈老爷的话一定不错。并且他自己也明明看到自从镇上有了洋纱、洋布、洋油这一类洋货，而且河里更有了小火轮船以后，他自己田里的东西就一天一天不值钱，而镇上的东西却一天一天贵起来。

——摘自茅盾《春蚕》

材料二：夫计划之确切，组织之严密，技术之专精，会计之优良，以及一切管理之科学化，因为经营工业应备诸条件。然此仅能指环境优越而一时便利之某一地，或某一业而言，或指资本雄厚之某一工厂或某一公司而言。若估量整个民族工业，则其先决问题又当别论。于此吾人应特加注意者，工业上局部或个别之兴隆，在整个民族工业或大规模基本工业未能建立以前，均将如昙花一现，不久即销声匿迹。例如上海之我国纺纱业与缫丝业，虽曾盛极一时，而其前途仍至渺茫。故提倡国货最根本之办法，在乎奠定民族工业之基础。而建立中国民族工业之前程，厥惟三端：曰民族独立。曰政治清明。曰农村繁荣。

——摘自陈翰笙《建立中国民族工业之前提》

材料三：这座城市曾创下“三天一层楼”的“深圳速度”，但如今，这座城市却开始一心一意地追求“慢”。2008年12月7日，联合国教科文组织授予这座城市“设计之都”的称号，这是全世界第六个获此殊荣的城市，也是中国首个获得这一荣誉的城市。这个演绎了无数速度神话的城市，正在以自己的方式沉淀下来。“时间就是金钱，效率就是生命”的标语在深圳蛇口矗立了三十年。过去，深圳人在它的激励下，创造了“深圳速度”，吹响了改革开放的号角。现在，深圳人经过反思，开始了由“速度深圳”向“创意深圳”转型。未来，深圳人将赋予时间和效率全新的意义，让深圳再次先行。

——摘自腾讯网《今天的“深圳速度”》

根据分式的基本性质，分式$\frac{-a}{a-b}$可变形为（          ）