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下面几种燃料在产生能量方面最高效的是()
寻找最有效、最经济的汽车燃料
当一些研究人员集中精力研究汽车并改进汽车系统和材料时，另一些人的研究重点则放在汽车的燃料上。至少在一定情境下，改进汽车和提炼燃料是携手并进的。在研制出催化转化器之后，石油工业必须使汽油变成无铅汽油。含铅汽油排放的废气中有铅，使转化器中的金属涂上一层膜，导致这些金属失效。由于铅已与癌症联系起来并能引起儿童神经系统损伤，因此无铅汽油是针对汽车污染的一项重要发展。
研究人员继续寻找改善汽油的办法。提炼原油以产生汽油涉及给石油加热并在石油挥发过程中提取各种碳氢化合物。有一些碳氢化合物是容易挥发的轻量分子，另一些碳氢化合物则重一些，它们有形成沉积物和微粒的趋势，并可能引起癌症。
石油公司通过多使用重量等级居中的碳氢化合物——既不很轻也不很重的碳氢化合物，就能创造出污染较少的汽油。提炼厂也能分解或“裂化”较重的碳氢化合物以产生较轻的化合物。一些汽油添加剂在其结构中含有氧原子。这有助于促使燃料燃烧更完全。
研究人员也在调查除汽油之外的其他燃料。甲醇排放的污染物数量较少，这些污染物通常与汽油燃烧有关。但是甲醇的潜能比汽油少，而且甲醇更难点燃。甲醇也能腐蚀许多金属。最后，甲醇产生一种刺激眼睛、鼻子和咽喉的有害化合物，被认为能引起癌症。从积极方面来说，甲醇比汽油燃烧得更完全，在与15%的汽油混合在一起形成一种叫M-85的燃料时，这种新燃料的启动性能令人满意。一种使用“灵活燃料”的引擎既能烧汽油也能烧甲醇，或者同时烧两种燃料。特殊传感器能决定使用哪一种燃料，并能把这个信息传达到中央电脑系统。
天然气是专家们认为能代替汽油的另一种储量丰富的燃料。天然气主要由甲烷气构成，比汽油便宜，也比汽油清洁得多。这种燃料的主要缺点是，不像汽油和甲醇，天然气在正常的气温和气压下无法以液态存在。天然气必须装在压力罐中，或者液态时要装在绝缘罐中——这是消费者可能拒绝的汽车设计之外的陌生附加物。加注天然气最多可能需要几个小时的时间。
一些科学家对把氢气作为一种未来的燃料感兴趣。氢燃烧比其他燃料燃烧都更清洁，而且容易生产。但是在氢气能广泛用于汽车之前，必须先解决复杂的技术问题。
电车安静，实际不排放任何废气。但是，电车用以获取能源的电池通常含有有害的化学物质。在电池被抛弃后这些化学物质就变成了污染物。由于电池供应的能量不如汽油燃烧产生的能量大，因此今天的电车不可能像汽油驱动的车辆跑得那样远或那样快。此外，电池必须经常充电，充电所需的能源来自发电厂，而发电厂本身也是污染源。尽管如此，在像加利福尼亚这样一些已制定零排放法的地区，电车是满足零排放要求的可能选择。
设法使汽车更清洁的继续不断的探索是对工程师以及化学家、材料科学家和技师提出的严峻挑战。我们的夙愿是维护汽车给我们发达的世界带来的行动自由。而目前这种广泛探索同我们的夙愿一起，反映出我们对环境所给予的新的和强烈的关注。
无铅汽油代表着在寻找更清洁燃料方面的一种飞跃，是因为()
Part A
Directions: Read the following four texts. Answer the questions below each text by choosing A, B, C or D . Mark your answers on ANSWER SHEET 1.
UN Secretary-General Kofi Annan visited the troubled Darfur region of western Sudan Thursday to consider ways to end the humanitarian crisis. More than a million people have been displaced in Darfur because of violence that human rights groups blame on government-backed militias.
Kofi Annan spoke with tribal and women leaders about the problems facing refugees in a camp called Zam-Zam, outside the city of E1-Feshir. The leaders said they were afraid to return home because of possible attacks by the Janjaweed militias. But overall, they said, aid groups were looking after them relatively well in the camp.
From there, the secretary-general and his delegation went to a camp just 30 minutes away where aid workers said the security and living situation was more desperate. But' the refugees were nowhere to be found. U.N. officials said some 4, 000 refugees, called internally displaced persons, or IDPs, had been in the camp the night before but they had been moved by Sudanese authorities. Jan Egeland, the U. N. 's undersecretary-general of humanitarian affairs, said the U.N. did not appreciate the authorities' actions. "But it was in our program actually to show the secretary-general and the secretary-general wanted to see how IDPs live when there are no services" ,"And this was such a place."
Mr. Egeland was then risked ff this was a deliberate ploy by Sudanese authorities. "I'm sure it has happened before and I'm sure it will happen again. "The refugees moved to another camp are among the one million people in Darfur driven from their homes by Janjaweed militias.
Human rights groups charge that the ethnic-Arab militias have been used by the government to terrorize the Darfur's civilian population, which is ethnic-African, as part of efforts to put down an armed rebellion. Sudanese authorities deny supporting the Janjaweed and say they are working to disarm them. Until recently, they allowed little access to the region by aid workers.
The conflict has given rise to what the U.N. calls the world's worst humanitarian crisis today. Refugees face hunger, epidemics (传染病)and continued attacks in camps in Darfur or over the border in Chad. From Darfur, Mr. Annan flew to Chad's capital, Ndjamena, for more discussions on the Darfur crisis. He is expected to return to Sudan's capital, Khartoum, Friday.
UN Secretary-General Kofi Annan ______.
You may all be aware of the fact that today's workplace is largely unstable—people get laid off and job hop constantly, and in general, staying anywhere more than five years is a career liability. Your learning curve flattens out so much that you're not gaining skills fast enough to stay competitive in the field.
In this environment, training is worth more than a promotion or a raise, and in fact, you'd do well to make a trade if someone offers you either. Training is the new currency of the workplace. Here are four reasons why.
First, believe it or not, the promotions you have desired for are stressful.
When you get offered a promotion, it's supposed to be a reward for good work. But in fact, most promotions distract you. Think about it：You're creating a career path that's customized to your skills, strengths, and personal goals. How could anyone else create a path that's right for you？Unfortunately, most companies structure a single corporate ladder and promote people upward whether it's good for them or not.
In fact, most people do good work and then get promoted into a position they've shown no aptitude for. This is most pronounced when, say, a creative person or technical person gets promoted into management. In fact, most promotions are so misguided they're more stressful than divorce.
My second point is about pay rise．Surprisingly, it can be neglected.
What do you get in exchange for taking the huge risk of leaving something you're good at to do something you're unproven at？What do you get in exchange for distracting your personal plans to follow someone else's path？A 3 percent raise(on average), or 10 percent if you're lucky？
Let's say you get a 10 percent raise. If you're earning $50,000, that's $5,000. After taxes it's around $3,500—if you even stay in the job for another year. That amount of money won't change your life, and even if you think it will, consider all the extra hours you'll be working because you got promo
Third, mentors make a real difference.
What will change your life？Mentoring. People who have a mentor are more successful than people who don't, across the board. For example, people with a mentor are 25 percent more likely to reach their next career goal than people who don't have mentors.
So one thing you could do is spend less time gunning for that promotion and more time focusing on what you need to do to get a mentor. For example, ask good questions of the people you admire, and spend extra time getting to know people outside of your core group of coworkers.
It would be great if you go to those advisory centers, which is a good choice as you can expect professional advice there. And you could always take the money and hire a career coach.
Let's come to our last point, training creates stability.
You can trade money for training, though, and that's what you should do. There's no job stability in the workplace today, so you have to count on yourself by being very desirable to employers. You do this by getting lots of training, and mentors to guide you on how to use that training.
There's a huge range of training available today—you can get trained in how to deal with your email, how to connect better to people you speak to, and how to transit from college to adulthood. Have your company pay for this sort of training — it's the kind that changes your life.
While a promotion actually makes your life more unstable, training creates more stability in your life. And that, rather than more money or a promotion, should be the real reward for performing well in your job.
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