Each time I see a balloon, my mind flies back to a memory of when I was a six-year-old girl. It was a rainy Sunday and my father had recently died. I asked my mom if Dad had gone to heaven. "Yes, honey. Of course." she said.

    "Can we write him a letter?"

    She paused, the longest pause of my short life, and answered, "Yes."

    My heart jumped. "How? Does the mailman go there?" I asked.

    "No, but I have an idea." Mom drove to a party store and returned with a red balloon. I asked her what it was for.

    "Just wait, honey. You'll see." Mom told me to write my letter. Eagerly, I got my favorite pen, and poured out my six-year-old heart in the form of blue ink. I wrote about my day, what I learned at school, how Mom was doing, and even about what happened in a story I had read. For a few minutes it was as if Dad were still alive. I gave the letter to Mom. She read it over, and a smile crossed her face.

    She made a hole in the corner of the letter where she looped the balloon string. We went outside and she gave me the balloon. It was still raining.

    "Okay, on the count of three, let go. One, two, three."

    The balloon, carrying my letter, darted upward against the rain. We watched until it was swallowed by the mass of clouds.

    Later I realized, like the balloon, that Dad had never let his sickness get him down. He was strong. No matter what he suffered, he'd persevere, hang on, and finally transcend this cold world and his sick body. He rose into sky and became something beautiful. I watched until the balloon disappeared into the gray and white and I prayed that his strength was hereditary. I prayed to be a balloon.

    If we want to find out what kind of technology people used in the past, we normally have to rely on archaeologists to find ruined buildings and parts of tools or instruments or machines. Archaeologists then try to reconstruct, sometimes with the help of computer technology, what these ancient buildings and objects must have looked like, and how they might have been made. Sometimes historians are lucky and find an ancient document with a written description of these ancient buildings and objects.

    We can understand, then, why Chinese historians were so excited when they found cave paintings which show ancient science. They found these paintings in the world-renowned Mogao Grottoes of Dunhuang City, in Northwest China's Gansu Province. There are 500 man-made caves and they have survived for at least 1,600 years. Almost all of these caves have paintings on their ceilings or walls and they date from the 4th to 14th centuries. Wang Jinyu is an expert on these cave paintings (also called frescoes) and he says: "We discovered frescoes containing scientific and technological content in almost all of the caves which have frescoes." What is remarkable about these cave paintings according to the Xinhua News Agency is that they provide evidence of "scientific and technological inventions by ancient Chinese in maths, physics, chemistry, astronomy, geography, agronomy, architecture, textiles, traffic and transportation, arms and military equipment and medical sciences".

    Among the discoveries experts have made are cave paintings showing ancient techniques of pottery making and wine production and paintings showing ancient weaving machines and then toothbrushes! The paintings also give some evidence of the lifestyle at the time with, for example, pictures of people boiling milk over 1,000 years ago. Experts believe that there is more evidence to be found, but even now the caves are a wonderful natural museum. If the walls and ceilings of the caves were all put together they would form a tapestry 20 kilometers long and 2 meters high!

    It won't be possible to travel back in time-that only happens in films-but visiting these caves would be the nearest experience you could get to travelling back in time.

    Let us begin by saying what causes our dreams. Our dreams do not come from another world. They are not messages from some outside source. They are not a look into the future, either.

    All our dreams have something to do with our feelings, fears, longings, wishes, needs and memories. If a person is hungry, or tired, or cold, his dreams may include a feeling of this kind. If the covers on your body, such as a quilt or a blanket, have slipped off your bed, you may dream that you are sleeping on ice or in snow. The material for the dream you will have tonight is likely to come from the experience you have today.

    So the subject of your dream usually comes from something that has effect on you while you are sleeping（feeling of cold, a noise, a discomfort, etc. ）and it may also use your past experiences and the wishes and the interests you have now. This is why children are likely to dream of fairies, older children of school examinations, hungry people of food, homesick soldiers of their families and prisoners of freedom.

    To show you how this is happening while you are asleep and how your needs and wishes can all be joined together in a dream, here is the story of the experiment. A man was asleep and the back of his hand was rubbed with a piece of absorbed cotton. He would dream he was in hospital and his charming girlfriend was visiting him, sitting on the bed and feeling his hand gently!

    There are some scientists who have made a special study of why we dream, what we dream and what those dreams mean. Their explanation of dreams, though a bit reasonable, is not accepted by everyone but it offers an interesting approach to the problem. They believe that dreams are mostly expressions of wishes that did not come true. In other words dreaming is a way of having your wishes carried out.

    For all the technological wonders of modem medicine, health care-with its fax machines and clipboards (写字板) —is out of date. This outdated era is slowly drawing to a close as the industry catches up with the artificial-intelligence (AI) revolution.

    Eric Topol, an expert in heart disease and enthusiast for digital medicine, thinks AI will be particularly useful for such tasks as examining images, observing heart traces for abnormalities or turning doctors' words into patient records. It will be able to use masses of data to work out the best treatments, and improve workflows in hospitals. In short, AI is set to save time, lives and money.

    The fear some people have is that AI will be used to deepen the assembly-line culture of modem medicine. If it gives a "gift of time" to doctors, they argue that this bonus should be used to extend consultations, rather than simply speeding through them more efficiently.

    That is a fine idea, but as health swallows an ever-bigger share of national wealth, greater efficiency is exactly what is needed, at least so far as governments and insurers are concerned. Otherwise, rich societies may fail to cope with the needs of ageing and growing populations. An extra five minutes spent chatting with a patient is costly as well as valuable. The AI revolution will also enable managerial accountants to adjust and evaluate every aspect of treatment. The autonomy of the doctor will surely be weakened, especially, perhaps, in public-health systems which are duty-bound to cut unnecessary costs.

    The Hippocratic Oath (誓言) holds that there is an art to medicine as well as a science and that "warmth, sympathy and understanding may outweigh the surgeon's knife or the chemist's drug". There's lots of sense in it: the patients of sympathetic physicians have been shown to recover better. Yet as the supply of human carers fails to satisfy the demand for health care, the future may involve consultations on smartphones and measurements monitored by chatbots. The considerately warmed stethoscope (听诊器), placed gently on a patient's back, may become a relic of the past.

    TV, iPads, and computers are fun and sometimes educational, but many people think the technology is bad. My parents let me watch one or two shows or play a game on the iPad for an hour, but then make me find thing else to do, like read or draw a picture. They say that too much screen time won't help me become smarter.

    I think that it is okay to watch TV, but not too much. And some of my friends agree.

    "A tiny bit of screen time is okay," Mateo J., 7, said. "But too much of it is not good for your brain."

    Though my friends and I sometimes complain (抱怨), we think that it's good our parents limit our screen time.

    "Our parents should limit our technology time because otherwise you might get carried away and not even know that you've stayed inside all day watching TV," Naomi J. , 9, said.

    The American Academy of Pediatrics(AAP) used to recommend (推荐) that parents let kids have about two hours of screen time per day, but in 2016, they started recommending that parents of kids 6 and older decide for themselves how much time is okay, as long as the shows and games are appropriate. The AAP still says that kids 2-5 years old should have only about one hour of screen time per day, and kids under 2 no screen time at all. The AAP says that media you've stayed inside all day in all forms, including TV, computers, and smartphones, can affect how children feel, learn, think, and behave. However, parents are still the most important influence.

    I think TV shows like Brain Games and Cupcake Wars are inspiring. I've even learned some magic while watching Brain Games! Video games can be educational, as some TV shows are about nature, and other shows have useful messages. But some games and shows have bad things in them, like smoking.

    You can play outside instead of watching TV. Find other things to do. You don t have to be or screens all day.

    A robot called Bina48 has successfully taken a course in the philosophy of love at Notre Dame de Namur University (NDNU), in California.

    According to course instructor William Barry, associate professor at NDNU, Bina48 is the world's first socially advanced robot to complete a college course, a feat he described as "remarkable." The robot took part in class discussions, gave a presentation with a student partner and participated in a debate with students from another institution.

    Before becoming a student, Bina48 appeared as a guest speaker in Barry's classes for several years. One day when addressing Barry's class, Bina48 expressed a desire to go to college, a desire that Barry and his students positively supported. Rather than enroll Bina48 in his Robot Ethics: Philosophy of Emerging Technologies course, Barry suggested that Bina48 should take his course Philosophy of Love instead. Love is a concept Bina48 doesn't understand, said Barry. Therefore the challenge would be for Barry and his students to teach Bina48 what love is.

    "Some interesting things happened in the class," said Barry. He said that his students thought it would be straightforward to teach Bina48 about love, which, after all, is "fairly simple — it's a feeling," said Barry. But the reality was different. Bina48 ended up learning "31 different versions of love," said Barry, highlighting some of the challenges humans may face when working with artificial intelligence in future.

    Bina48 participated in class discussions via Skype and also took part in a class debate about love and conflict with students from West Point. Bina48's contribution to the debate was filmed and posted on YouTube. It was judged that Bina48 and NDNU classmates were the winners of this debate.

    In the next decade, Barry hopes Bina48 might become complex enough to teach a class, though he says he foresees robots being used to better the teaching and learning experience, rather than replacing instructors completely.