People have been raising pigeons (鸽子) for about 10,000 years. And pigeon keepers use different kinds of pigeons for different1. Some people use pigeons for2. For example, in parts of the world, people cook a special meal with pigeon to celebrate the New Year. Some people also3pigeons because they look especially 4. There are many interesting kinds of “pretty” pigeons. Different kinds of pigeons have interesting features (特点)5 long, soft tails or designs on their heads. The6of these kinds of pigeons enter them in7and the best looking pigeons are chosen to win prizes.

    But pigeons have many other8too. Pigeons can fly a long way without growing9. They also have another10sense.No matter how far from home they are, pigeons can usually fly back to where they11. This is often called a “homing sense”. This sense makes them good for carrying 12.

    In many cities around the world, pigeons live in special houses,13pigeon keepers spend a lot of money and time14their birds. When someone has a very good pigeon, he is very15. He may also have a way to make money. But this is not usually the main16people keep pigeons. For some people, they keep pigeons as a hobby.

    People17their pigeons so much that they even take them18when they move to a new country. They19these birds as their children. “When you are looking at a pigeon in the sky you feel20. It is the best feeling you have in a strange country,” a pigeon lover says.

    I fell in love with Yosemite National Park the first time I saw it, when I was 13. My parents took us there for camping. On the way out, I asked them to wait while I ran up to E1 Capitan, a 1rock of 3,300 feet straight up. I touched that giant rock and knew2I wanted to climb it. That has been my life's passion ever since—  3the rocks and mountains of Yosemite. I've long made Yosemite my 4.

    About 15 years ago I started seeing a lot of 5, like toilet paper, beer cans, and empty boxes, around the area. It's 6me why visitors started respecting the place 7and treated such a beautiful home-like place this way.

    I tried 8trash (垃圾) myself, but the job was too big. I would9an hour or two on the job, only to find the area trashed all over again weeks later. Finally, I got so10it that I decided something had to change.

As a rock-climbing guide, I knew 11about organizing any big event. But in 2004, together with some climbers, I set a date for a 12. On that day, more than 300 people 13. Over three days we collected about 6,000 pounds of trash. It was amazing how much we were able to 14. I couldn't believe the15we made—the park looked clean!

    Each year volunteers come for the cleanup from everywhere. In 2007 alone, 2,945 people 1642,330 pounds of trash.

    I often hear people 17about their surroundings. If you are one of them, I would say the only way to change things is by 18rather than complaining. We need to teach by 19. You can't blame others 20you start with yourself.

    Almost everyone wants to get smarter. We struggle to improve our 1, intelligence and attention. We drink cup after cup of coffee to help us 2 the day.

    3, a new study published in Current Directions in Psychological Science warns that there are 4 to how smart humans can get.

    Each of our body parts develops in a certain way for a reason. 5 we are not 3 meters tall 6 most people's hearts are not strong enough to send 7 up that high. Scientists say that our thinking ability works in the same way. A baby's brain size is limited by a series of 8 , such as the size of the mother's pelvis(骨盆). If our brains developed to be bigger, there could be more 9 during childbirth.

    The study of Jews, who have an average IQ much 10 than other Europeans, showed they were more 11 to develop diseases of the 12 system. This might be because of their increased brainpower.

    If intelligence cannot be improved, can we at least get better at 13? Not really, say scientists. They studied 14 like caffeine(咖啡因) that improve attention. They found the drugs only helped people with serious 15 problems. For those who did not have trouble paying attention, the drugs could have the 16 effect. Scientists say that this suggests there is a(n) 17 limit to how much people can or should concentrate.

    Our memory is also a "double-edged sword". People with extremely good memories could 18 having a difficult life because they cannot 19 bad things that happen to them.

    Thomas Hills, one of the authors of the paper, said that 20 all the problems in trying to get smarter, it's unlikely that there will ever be a "super mind".

    Technology is playing a vital role in preservation and ecology research. Drones (无人机) hold huge 1 in the fight to save the world's remaining wildlife from extinction. So researchers can now track wild animals through dense forests and monitor whales in vast oceans. It's estimated that up to five living species become extinct every day, making it urgent that universities develop new technologies to capture the data that can persuade 2 to act.

    The British International Education Association hosted a conference in January to 3 the importance of technological solutions in protecting vulnerable (易受伤害的) species and ecosystems. Speakers underlined how technology can help 4: drones can circle high above the ocean to spot whales, while certain cameras can identify members of an individual species.

    According to Claudio Sillero, biology professor at Oxford University, technology is changing how preservation research is done — but it's in a(n) 5 way. As technology gets better and cheaper, researchers become better at doing what they were already doing. 6, remote sensing used to be a very technical tool but is now widespread, and everyone uses global positioning system (GPS) for surveying.

    But teaching preservation and ecology courses in university 7. Some teach drone surveying methods in depth while others don't even mention them. "The fact is, using drones is quite a(n) 8 to the interdisciplinary (跨学科的) 'unknown' of engineering, and potentially an area where lecturers may not feel confident to teach yet," Serge Wich, an expert in primate biology says. "Students are taught about 9 technologies such as automatic sound recorders, but drones are often missing from university teaching. Consequently, drone use among researchers is still fairly 10 and focused on getting photos."

    Wich's team of researchers used techniques to develop a fully automated drone technology system that 11 and monitors the health of endangered animals globally. It's designed to be cheap, stable and simple to use, so that local communities in developing countries can operate it 12 without technical background. Yet it's not more widely used on the grounds of researchers' lack of skills to use this technology. In biology, where drones are used, few can program an algorithm (算法) specifically for their preservation or research problem. "There's much that needs to be done to 13 those two worlds and to make AI more user-friendly so that people who can't program can still use the technology," Wich says.

    14, the sad truth is that better technology alone will not save any more species from dying out, Greengrass warns. "As human populations increase, so do threats and pressure on wild places. Preservationists are 15 for not doing enough but it's often an issue of people, conflict and governance." Technology may help provide far greater knowledge, but governments still need to act.

    Wildlife has been greatly threatened in the modem age. There are species (物种) that are 1 every day. The white-naped crane is a typical example. So scientists are trying their best to 2 the species from going out of existence.

    Chris and Tim work at a zoo, helping endangered cranes with their 3. Emma, a female crane, has been in their 4 since she arrived in 2004.

    Born at an international crane foundation, Emma was 5 by human caretakers. This led to an unexpected 6, though she had a wonderful time there. Emma had 7 taken herself as a crane and become deeply attached to humans. She 8 to live with male cranes, and even had a 9 for killing some of them, which made it 10 for her to become a mother.

    11, the two zookeepers didn't want to see the extinction (灭绝) of this precious species. With their patience and efforts, they successfully developed a 12 of artificial breeding (人工繁殖) and natural reproduction. This 13 Emma to give birth to five baby cranes.

    The two keepers are proud of their productive work. But before they can be 14, more efforts must be made, because the population of the crane in the wild is on the 15, and many other species appear headed toward extinction. 16, not everyone has realized that wildlife has thoughts, feelings, and most importantly, equal rights to survive.

    How can we 17 the ever-widening gap that separates us from other animals? Chris and Tim offered us the 18: human beings took it for granted that their 19 held all the solutions, but maybe their hearts can be a better 20.

Many things happen when people are ageing. Apart from the greying hair and wrinkled skin, there is a(n) 1 change which comes with older age. When humans reach their later years, they favour more long-term 2 and their social cirele is reduced.

Now, for what appears to be the first time, scientists have seen the same 3 in another species. Twenty years of observations of chimpanzees (猩猩) reveal that older males choose to keep contact with their 4 friends at the expense of other relationships.

The researchers studied 78,000 hours of observations made between 1996 and 2016 that followed the social 5 of 21 male chimpanzees between the ages of 15 and 58 years old. They classified the chimps' 6 depending on the amount of time they sat with others and groomed (梳毛) them. They then rated (分类) the various pairings as mutual (相互的) friendships, where both chimps seemed to enjoy the relationship;  7 friendships, where one chimp was more keen to be friends than the other; and non-friendships, where neither chimp showed 8 the other.

When the scientists looked at the 9 of friendships, they found that the older chimps had more mutual friendships and fewer one-sided friendships than younger chimps. Another 10 seen in older humans was also spotted in the chimps. As the males got older, their levels of 11 gradually become less, meaning they started fewer fights and tended to threaten others in their group less often.

The observations have left the researchers 12. According to an idea in psychology known as socio-emotional selectivity theory, older humans prefer more 13 relationships because they are aware that time is running out. However many animal experts argue that chimpanzees 14 the human sense of mortality (死亡) , suggesting something else is driving the behaviour.

Robin Dunbar, a professor of evolutionary psychology at the University of Oxford, said in humans, the 15 social circles with age is due to declining social motivation to get out and meet people combined by lack of opportunity. In chimpanzees, as older males compete less for mates, they may focus on close, reciprocal (互惠的) relationships with trusted partners, he said.