In the last few years the popularity of eBooks has exploded．The advantages are clear：You can carry as many books with you as you want．You can simply download every book you like and instantly start reading instead of having to wait for the book to arrive by mail．

    However，one thing hadn't changed．If you wanted to rent a book you were still forced to use hardcopy books．Until now that is, Amazon．com recently announced the start of a new program where you can rent eBooks．

Where to rent eBooks？

    As mentioned before，Amazon．com is the first and currently the only retailer (零售商) that has a program in place for renting eBooks． Luckily，Amazon is the largest online retailer in the world and their eBook assortment (分类) is massive．They are also the producer of the Kindle，the most popular Reader，which means you can be sure that the eBooks you rent will work．

You can currently only rent Textbooks．But this is likely to change as soon as word gets out that you can save money by renting eBooks.

Why rent eBooks at Amazon?

* Save money：Save up to 80% of the normal price of the eBook．

* Decide how long you rent：From 30 days to 360 days，you decide how long you want it．You can extend the time by as little as a day．Or simply buy the eBook if you want to keep it after all．

*Use any device：If you rent an eBook from Amazon，you can read it on your PC，Mac，iPad，iPhone，Android device，Windows Phone 7．Blackberry．or Kindle．

* Keep your notes：Do you like to keep annotations (注释) and highlights in your eBooks？Don't worry．You can always revisit your notes and highlights through Amazon．com．

How to rent eBooks？

    Simply search for the eBook you want to rent on Amazon．com and select the "Rent eBooks" option. After that，a new page will open where you can select how long you'd like to rent the eBook．You can read eBooks for a period of 30 to 360 days．

    You decide how long you need the eBook．If you later find out you need it for longer, you can simply extend the time．Or buy it for the normal price whenever you want.

    Once you've chosen the time you want to rent the eBook，you simply go to checkout．Or you can use the "Rent now" button．

    Women are friendly．But men are more competitive．Why? Researchers have found it's all down to the hormone oxytocin （荷尔蒙催生素）．Although known as the love hormone, it affects the sexes differently．

"Women tend to be social in their behavior．They often share with others．But men lend to be competitive．They are trying to improve their social status," said Professor Ryan．

    Generally, people believe that the hormone oxytocin is let out in our body in various social situations and our body creates a large amount of it during positive social interactions （互动） such as falling in love or giving birth．

But in a previous experiment Professor Ryan found that the hormone is also let out in our body during negative social interactions such as envy．

    Further researches showed that in men the hormone oxytocin improves the ability to recognize competitive relationships, but in women it raises the ability to recognize friendship．

Professor Ryan's recent experiment used 62 men and women aged 20 to 37．Half of the participants（参与者）received oxytocin．The other half received placebo （安慰剂）．

    After a week, the two groups switched with participants．They went through the same procedure with the other material．

    Following each treatment, they were shown some video pictures with different social interactions．Then they were asked to analyze the relationships by answering some questions．The questions were about telling friendship from competition．And their answers should be based on gestures, body language and facial expressions．

    The results indicated that, after treatment with oxytocin, men's ability to correctly recognize competitive relationships improved, but in women it was the ability to correctly recognize friendship that got better．

    Professor Ryan thus concluded: "Our experiment proves that the hormone oxytocin can raise people's abilities to better distinguish different social interactions．And the behavior differences between men and women are caused by biological factors （因素） that are mainly hormonal．"

B

    Cities usually have a good reason for being where they are, like a nearby port or river. People settle in these places because they are easy to get to and naturally suited to communications and trade. New York City, for example, is near a large harbour at the mouth of the Hudson River. Over 300 years its population grew gradually from 800 people to 8 million. But not all cities develop slowly over a long period of time. Boom towns grow from nothing almost overnight. In 1896, Dawson, Canada, was unmapped wilderness(荒野). But gold was discovered there in 1897, and two years later, it was one of the largest cities in the West, with a population of 30,000.

    Dawson did not have any of the natural conveniences of cities like London or Paris. People went there for gold. They travelled over snow-covered mountains and sailed hundreds of miles up icy rivers. The path to Dawson was covered with thirty feet of wet snow that could fall without warming. An avalanche(雪崩) once closed the path, killing 63 people. For many who made it to Dawson, however, the rewards were worth the difficult trip. Of the first 20,000 people who dug for gold, 4,000 got rich. About 100 of these stayed rich men for the rest of their lives.

    But no matter how rich they were, Dawson was never comfortable. Necessities like food and wood were very expensive. But soon, the gold that Dawson depended on had all been found. The city was crowded with disappointed people with no interest in settling down, and when they heard there were new gold discoveries in Alaska, they left Dawson City as quickly as they had come. Today, people still come and go — to see where the Canadian gold rush happened. Tourism is now the chief industry of Dawson City — its present population is 762.

    In recent years, much of the sea ice that polar bears use as a hunting platform for seal meals has melted, forcing some bears — particularly young males — farther north or onto land, where they are not as skilled at hunting. When stuck on land for months, a polar bear typically is forced to survive on its own fat reserves.

    The bears were listed earlier this year as a threatened species under the U. S. Endangered Species Act as populations have declined. Meanwhile, snow geese are booming near the western Hudson Bay, and there are in fact too many of them. Their eggs can be a good food source. The geese nest on tundra (冻原；苔原) that some bears have retreated to.

    "Over 40 years, six subadult (接近成年的) male bears were seen among snow goose nests, and four of them were sighted after the year 2000," says Robert Rockwell. "I've seen a subadult male eat goose eggs whole or press its nose against the shell, break it, and eat the contents."

    Ice is melting, on average, 0.72 days earlier each year in the region studied. Snow geese are hatching eggs about 0.16 days sooner each year, according to Rockwell and his graduate student Linda Gormezano. Current trends indicate that the arrival of polar bears will correspond to the average hatching period in 3.6 years, and egg consumption could become a viable option, which the researcher concluded in a statement released today.

    A polar bear, the largest land carnivore (食肉动物), would need to consume the eggs of 43 nests to replace the energy gained from the average day of hunting seals, but Rockwell and his colleagues figure that while many polar bears may starve in coming years, the resourceful animals just might survive disappearance.

    Polar bears survived a warm period about 125,000 years ago, when sea level was 12 to 18 feet higher than it is now and trees lived above the Arctic Circle, the scientists point out.  "They've been through the warm period before，" Rockwell said.

    The polar bears' potential movement to a diet of more eggs brought to mind a quote by Ilkoo Angutikjuak, an Inuit who lives in the Canadian province of Nunavut, in the February 2008 issue of Natural History magazine, Rockwell said. Angutikjuak said: "The animals will adapt. I've heard that because they depend on sea ice, polar bears will disappear, but I don't believe it. They are very adaptable. As the sea ice changes, polar bears might get skinnier and some might die, but I don't think they will disappear."

    Tablets are really useful devices, but their big screens always make them as a burden to carry around without a bag. Wouldn't it be great if there were a phone with the powers of a tablet that could be folded up and fit neatly into the hand?

    Now something like a tablet-shaped but foldable phone is about to become available. In February, South Korean electronics company Samsung and China's Huawei both launched foldable phones, the Galaxy Fold and Huawei Mate X respectively. Mobile phone use has entered the "foldable future", The Verge noted.

    The technology could change our lives in significant ways. These devices, due to their bendable screens, give us the larger screens we want. Meanwhile, they still fit easily into the pocket. As USA Today noted, they're "the combination of a small tablet and smartphone, all in a single device".

    The technology could change other devices, too. For example, we could make TVs that stick to walls like posters, or fold up easily to hide away in drawers. In crowded modem cities, they will help us to maximize available space.

    In a keynote address, Samsung's senior vice president of mobile product marketing, Justin Denison, called the foldable screen "the foundation for the smartphone of tomorrow". "It's a blank canvas (画布) for us to do something beautiful together." he said.

    So is there nothing to stand in the way of the foldable future? According to tech news website Android Authority, the necessary displays were difficult to produce. In 2012, nine out of every 10 OLED (二极管) screens produced were imperfect. Today, that 10 percent rate has been improved to between 50 and 90 percent. However, at present these foldable devices are expensive. For example, the price of Huawei Mate X is 17,500 RMB. That's a price that few people will be able to afford.

    But if the foldable device isn't going to change the world overnight, there is no doubt that it is coming. Patrick Moorhead, an industry analyst told The Verge, "Few are debating if foldable or rollable mobile displays are the future of smartphones; the only question is when and by whom."