Mark Twain has been called the inventor of the American novel.And he surely deserves additional praise：the man who popularized the clever literary attack on racism.

     I say clever because anti­slavery fiction had been the important part of the literature in the years before the Civil War.H.B.Stowe's Uncle Tom's Cabin is only the most famous example.These early stories dealt directly with slavery.With minor exceptions，Twain planted his attacks on slavery and prejudice into tales that were on the surface about something else entirely.He drew his readers into the argument by drawing them into the story.

     Again and again，in the postwar years，Twain seemed forced to deal with the challenge of race.Consider the most controversial，at least today，of Twain's novels，Adventures of Huckleberry Finn.Only a few books have been kicked off the shelves as often as Huckleberry Finn，Twain's most widely read tale.Once upon a time，people hated the book because it struck them as rude.Twain himself wrote that those who banned the book considered the novel “trash and suitable only for the slums(贫民窟)．”More recently the book has been attacked because of the character Jim，the escaped slave，and many occurences of the word nigger.(The term Nigger Jim，for which the novel is often severely criticized，never appears in it.)

     But the attacks were and are silly—and miss the point.The novel is strongly anti­slavery.Jim's search through the slave states for the family from whom he has been forcibly parted is heroic.As J．Chadwick has pointed out，the character of Jim was a first in American fiction—a recognition that the slave had two personalities，“the voice of survival within a white slave culture and the voice of the individual：Jim，the father and the man.”

There is much more.Twain's mystery novel Pudd'nhead Wilson stood as a challenge to the racial beliefs of even many of the liberals of his day.Written at a time when the accepted wisdom held Negroes to be inferior(低等的)to whites，especially in intelligence，Twain's tale centered in part around two babies switched at birth.A slave gave birth to her master's baby and，for fear that the child should be sold South，switched him for the master's baby by his wife.The slave's lightskinned child was taken to be white and grew up with both the attitudes and the education of the slave­holding class.The master's wife's baby was taken for black and grew up with the attitudes and intonations of the slave.

     The point was difficult to miss：nurture(养育)，not nature，was the key to social status.The features of the black man that provided the stuff of prejudice—manner of speech，for example—were，to Twain，indicative of nothing other than the conditioning that slavery forced on its victims.

Twain's racial tone was not perfect.One is left uneasy，for example，by the lengthy passage in his autobiography(自传)about how much he loved what were called“nigger shows”in his youth—mostly with white men performing in black­face—and his delight in getting his mother to laugh at them.Yet there is no reason to think Twain saw the shows as representing reality.His frequent attacks on slavery and prejudice suggest his keen awareness that they did not.

     Was Twain a racist？Asking the question in the 21st century is as wise as asking the same of Lincoln.If we read the words and attitudes of the past through the“wisdom”of the considered moral judgments of the present，we will find nothing but error.Lincoln，who believed the black man the inferior of the white，fought and won a war to free him.And Twain，raised in a slave state，briefly a soldier，and inventor of Jim，may have done more to anger the nation over racial injustice and awaken its collective conscience than any other novelist in the past century.

    Since 2008, hunters have illegally killed more than 3000 rhinos in South Africa. The International Union for Conservation of Nature warns that rhinos may die out by 2026. People who hunt and kill illegally are called poachers. The most effective way to watch for and prevent illegal hunting is from the air. However, piloted flights are too costly. Fortunately, some Spanish college students have invented a drone (无人机) that can observe more places than a plane.

    Arnau Garcia is an aeronautical (航空学的) engineering student at the Polytechnic Institute of Catalonia, in Spain. He says observers from the air have trouble finding poachers when they hide under the trees. Mr. Garcia and other students have worked with the drone manufacturer HEMAV to help find the hidden poachers. They make it by using the thermal camera, which is especially sensitive to body heat. Even when the poachers keep still, it can also keep track of them.

    The drone can fly in the wind up to 55 kilometers per hour. It has an autopilot system, so it memorizes the flight path. The drone also has a microphone, a video camera and a GPS system. These permit it to report accurately where a picture is taken. After each flight, the drone can bring back detailed information about where rhinos are found, the conditions of water and plants in the area, and the positions of suspected poachers.

    Experts say the drone can fly as far as 70 kilometers from the base. It means that it could quickly observe large areas for poachers. However, the same search operation would take days for human observers. Thanks to the drone, many poachers have been caught and the number of rhinos is on the increase. In addition, HEMAV has received an increasing number of orders for the drone. Even South African national park officials attempt to fill the air with drones.

    People all need friends because nobody wants to be lonely and a friend can help you in good and bad times. You've made friends since childhood, but you still don't know who your true friends are. Here are some signs to tell you if your friend is a true friend:

Always honest

    Honesty is important to keep a relationship alive. A true friend always tells you the truth. It may be hard sometimes but lying can destroy a friendship. It is important that your friend speaks honestly and never makes up stories.

______________

    There are always periods in your life when you have problems or difficulties. A true friend will always have time to listen to your problems and give advice. It may not be able to offer a solution to your problems but the fact that your friend made time to listen is a sign he/she cares for you. Your friend is not a true friend if he/she can never make time for you when you are in trouble. You also need to be reasonable and accept that your friend also has other things to do so he/she can't always listen immediately to your problems.

Always respectful

    A true friend will always respect your opinion no matter whether he/she agrees or not. Your true friend may disagree but never insists that he/she is correct.

Always understanding

    It is possible that some problems will arise between you and your friend. A true friend will always be forgiving and understanding even if it isn't his /her fault. We are all different people and we all make mistakes. A true friend is always forgiving and understanding because he/she doesn't want to take the risk of losing his/her best friend.

    It isn't often that zookeepers call on craftsman for help. But cold weather at the Wildlife SOS Elephant Conservation and Care Center in northern India was putting elephants at risk. So the center's staff joined forces with locals to find a creative way to keep the animals warm. Now the elephants are stepping out in style, thanks to volunteers who made use of their crafting talents to knit (编织) enormous sweaters to protect the animals.

    Wildlife SOS is a conservation group that has been taking action against animal cruelty and saving wildlife in danger since 1995. Their Elephant Conservation and Care Center is devoted to rescuing the large animals from abuse in circuses, illegal dealing, and other circumstances where they have been ignored or treated with extreme cruelty. There are currently 20 elephants living at the center, and the staff hope to take in 50 more of the creatures this year.

    Because most of the elephants housed at the center are recovering from injuries or are elderly and weak, they are particularly vulnerable to cold temperatures. When the staff reported near-freezing nighttime temperatures in the winter, volunteers from surrounding villages began knitting enormous sweaters to keep the elephants warm. The monumental sweaters are large enough to cover the elephants' backs, bellies, and legs.

    Making the sweaters is a big undertaking—each one takes approximately four weeks to create, with volunteers working together on the enormous clothes. Local villagers have already made sweaters for three of the 23 elephants on their own, each with a unique pattern and color.

    If you're also looking for something happy and heartwarming, this is it. The elephants usually wear blankets to keep warm during colder months and you can purchase a blanket for an elephant on the Wildlife SOS website.

    All too often, a choice that seems sustainable(可持续的)turns out on closer examination to be problematic. Probably the best example is the rush to produce ethanol(乙醇) for fuel from corn. Corn is a renewable resource —you can harvest it and grow more, almost limitlessly. So replacing gas with corn ethanol seems like a great idea. 

    One might get a bit more energy out of the ethanol than that used to make it, which could still make ethanol more sustainable than gas generally, but that's not the end of the problem. Using corn to make ethanol means less corn is left to feed animals and people, which drives up the cost of food. That result leads to turning the fallow land –including, in some cases, rain forest in places such as Brazil—into farmland, which in turn gives off lots of carbon dioxide (CO) into the air. Finally, over many years, the energy benefit from burning ethanol would make up for the forest loss. But by then, climate change would have progressed so far that it might not help.

    You cannot really declare any practice “sustainable” until you have done a complete life-cycle analysis of its environmental(环境的) costs. Even then, technology and public keep developing, and that development can lead to unforeseen and undesired results. The admirable goal of living sustainably requires plenty of thought on an ongoing basis.

    The arm bones of women who lived 7,000 years ago show a surprising level of strength-even higher than today's professional athletes. that's according to a first-ever study comparing prehistoric(史前的) bones to those of living people. The finding suggests a revision of history- the everyday lives of prehistoric women were filled with hard labor, rather than just sitting at home doing lighter tasks while the men struggled and fought for life.

    Before the study, there are no clear records describing how our ancient ancestors lived. It can be easy to forget that bone is a living tissue, one that responds to the difficulties we put our bodies through, "said lead author Alison Macintosh."Physical force and muscle activity both put pressure on the bone. The bone reacts by changing in shape, thickness and other aspects over time.

    Previous studies only compared female bones to contemporary male bones, the researchers said-and that's a problem, because the response of male bones to stress and change is much bigger than that of women. For instance, as humans moved from a hunter-gatherer lifestyle constantly on the move to a more settled agrarian(农耕的) one, changes can be observed in the structure of the shinbone(胫骨)- and these changes were much more evident in men.

    However, a comparison of the bones of prehistoric women to the bones of living female athletes can help us work out a more accurate picture of what those prehistoric women were doing. "By analyzing the bones of living people and comparing them to the ancient bones, we can start to explain the kinds of labor our ancestors were reforming, Macintosh said. What they found was that women's leg strength hasn't changed a great deal, but their arms used to be very powerful. Prehistoric women, the researchers found, had arm strength 11-16 percent stronger than those of modern rowers, and 30 percent stronger than those of non-athletes.