In its early history, Chicago had floods frequently, especially in the spring, making the streets so muddy that people, horses, and carts got stuck. An old joke that was popular at the time went something like this: A man is stuck up to his waist in a muddy Chicago street. Asked if he needs help, he replies,“No, thanks. I've got a good horse under me.”

    The city planners decided to build an underground drainage(排水) system, but there simply wasn't enough difference between the height of the ground level and the water level. The only two options were to lower the Chicago River or raise the city.

    An engineer named Ellis Chesbrough convinced the city that it had no choice but to build the pipes above ground and then cover them with dirt. This raised the level of the city's streets by as much as 12 feet.

    This of course created a new problem: dirt practically buried the first floors of every building in Chicago. Building owners were faced with a choice: either change the first floors of their buildings into basements, and the second stories into main floors, or hoist the entire bulidings to meet the new street level. Small wood-frame buildings could be lifted fairly easily. But what about large, heavy structures like the Tremont Hotel, which was a six-story brick building?

    That's where George Pullman came in. He had developed some house-moving skills successfully. To lift a big structure like Tremont Hotel, Pullman would place thousands of jackscrews(螺旋千斤顶) beneath the building's foundation. One man was assigned to operate each section of roughly 10 jackscrews. At Pullman's signal each man turned his jackscrew the same amount at the same time, thereby raising the building slowly and evenly. Astonishingly, the Tremont Hotel stayed open during the entire operation, and many of its guests didn't even notice anything was happening.

    Some people like to say that every problem has a solution. But in Chicago's early history, every engineering solution seemed to create a new problem. Now that Chicago's waste water was draining efficiently into the Chicago River, the city's next step was to clean the polluted river.

    A long time ago people thought that the sun went round the earth. In some countries people even said that the sun was a god(神). They thought the god drove across the sky each day on a golden horse. Now we know the earth goes round the sun. It takes the earth a year to go a circle(圈) round the sun. Today men even know how far it is for the earth to go round the sun. They tell us that the earth travels over a thousand miles a minute on its journey round the sun.

    The sun is really a star. It is much bigger than the earth and it is very hot. Some people have been to the moon but we know that no one can ever go to the sun. It is far too hot for people to live anywhere near it. The sun is three hundred thousand times heavier than the earth and more than million times larger.

    At times my mom has been uncomfortable seeing these qualities in me. For example, when I was 12, I went to Puerto Rico all by myself to stay with my grandmother for the summer. My mom was extremely nervous about it. She kept telling me how things were different in Puerto Rico, to always put on sunscreen, not to wander away from my grandmother, and other warnings. She helped me pack and did not leave the airport until she saw my plane take off.

    Despite her worries, she let me go on my own. As I moved into my teens, she continued to give me space to grow and learn, even when it might have been difficult for her. When I reached my senior year, I decided to move away for college. Once again I found that I differed from my peers: while many of them wanted to stay close to home, I couldn't wait to be out in the world on my own. While my mom may not have been happy at the thought of my going away, she was supportive and excited for me.

    One big thing I realized during my senior year when my mom granted me more freedom was that she actually believed in me and trusted me. That meant a lot. In most time of my life, and especially when I was little, the main person I tried to impress in my schoolwork or other things was my mother. I knew she expected nothing but the best of me. Sometimes it was hard to live up to her standards; getting a single B on my report card would make me feel bad because I knew she wanted me to have all A's.

    I know that her high standards have helped me stay focused on what's important, like education, and made me who I am. I am thankful for her support and involvement in my life. Most of all I respect her. She is the strongest woman I know and that's why I have turned out so strong and independent.

    More than a hundred years ago, two boys were fishing in a small river. They sat in a heavy-bottomed boat, each holding a long, bent pole in his hands and eagerly waiting for "a bite". When they wanted to move the boat from one place to another they had to push against a long pole into the bottom of the stream.

    "This is slow work, Robert," said the older of the boys. "Yes, Christopher, and it's hard work, too." answered Robert. "I think there's some better way of moving a boat."

    Christopher advised rowing it and Robert promised to make some paddles (桨). The next day Robert's aunt heard a great noise in her house. The two boys were there, busily working. "What are you making, Robert?" she asked. He told his plan. His aunt laughed and said, "Well done! I hope you'll succeed."

    After much work, they succeeded in making two paddle wheels. They were very rough, but strong and usable. They fixed each of these wheels to the end of an iron rod (长杆) which they passed through the boat from side to side. The rod was bent in the middle. When the work was finished, the old fishing boat looked rather strange, with a paddle wheel on each side. The boys lost no time in trying it. One of the boys could guide the boat while the other turned the paddle wheels.

    That night when Christopher went home, he told his father a wonderful story. "Robert Fulton planned the whole thing," he said, "and I helped him make the paddles and put them on the boat." When Robert Fulton became a man, he didn't forget his experiment with the old fishing boat. He kept on thinking and working, until at last he succeeded in making a boat with paddle wheels that could be run by steam. He's now honored as the inventor of the steamboat.

    When Johnny, a homeless man, spent his last $20, he wasn't looking at it as an investment — but it's about to pay him huge profits. After he helped a woman who ran out of gas, she returned the favor by raising a lot more on the Internet.

    Kate McClure, 27, was driving to visit a friend when she ran out of gas halfway. “He saw me pull over and knew something was wrong,” she wrote. “He told me to get back in the car and lock the doors. A few minutes later, he came back with a red gas can, using his last 20 dollars to make sure I could get home safe.”

    She couldn't repay him at that time because she had no cash with her. “I have been stopping by his spot for the past few weeks. I repaid him for the gas and gave him some clothes.”

    Kate decided to do more for him, so she started a crowdfunding(众筹) campaign on GoFundMe.com, and it quickly gained far beyond its initial $10,000 goal. When it reached $100,000, the fundraising page was shut down for a time at Johnny's request. Because he didn't want to seem like he was taking advantage of the situation. Finally, Kate said that she restarted it because the public interest had not decreased. She also added that Johnny planned to donate the rest to a good cause.

    According to the New York Post  Johnny wants to get a job at an Amazon warehouse and a department manager from the tech company has already reached out, saying he wants to help Jonny.

    A single dose(剂量) of an experimental vaccine(疫苗) can protect mice against the Zika(寨卡) virus, raising renewed hope of a vaccine for humans, say scientists. The US team say the results, published in Nature, are "striking" and should encourage research efforts.

    Tests in humans could begin in months. But even if these go well, a licensed vaccine for widespread use to protect those at most risk ­ such as pregnant women ­ would still be years away, experts advise. Zika has been spreading across Central and South America and, most recently, Africa. More than 60 countries and territories now have continuing transmission(传播) of the disease, which is carried by mosquitoes. The virus causes serious birth damages during pregnancy and has been declared a global public health emergency.

    Now, developing a vaccine for pregnant women to protect their unborn babies is an international research priority(优先事项). US scientists from the Walter Reed Army Institute of Research, the Beth Israel Deaconess Medical Center and Harvard Medical School tested two types of Zika vaccine in mice – one based on bits of genetic(基因的) code from the virus and another that is an inactive (and therefore harmless) copy of Zika. Both worked well, protecting every mouse that was immunised against the virus. In comparison, all of the mice not given the vaccine caught Zika after they were exposed to it.

    Researchers say they will push ahead with developing the needed virus vaccine. There are many existing vaccines for other disease that use this type of technology, while there are relatively few DNA­based vaccines. Of course, future tests will need to check the vaccine is safe and effective in humans, as well as how long the immunity might last.