The full moon climbs over the eastern horizon (地平线) and hangs like a huge orange globe in the sky. A few hours later, the moon is overhead but seems to have changed. The huge orange globe has become a small silver disk. What has happened? Why has the orange color disappeared? Why does the moon seem so much smaller and farther away now that it is overhead?

    The moon appears orange on the horizon because we view it through the dust of the atmosphere. The overhead moon does not really shrink as it moves away from the horizon. Our eyes inform us that the overhead moon is farther away. But in this position the moon is actually closer to our eyes than when it is near the horizon.

    The change in size is a trick our eyes and minds play on us. When the moon is low in the sky, we can compare its size with familiar objects. It is easy to see that the moon is much larger than trees or buildings, for example. When the moon is high in the sky, however, it is hard to compare it with objects on earth. Compared to the vastness of the sky, the moon seems small.

    There is another reason why the moon seems to shrink. We are used to staring at objects straight ahead of us. When an object is difficult to see, our eyes have to try to focus on it. When we move our heads back to look up, we will try hard again. Looking at something from an unaccustomed position can fool you into believing an object is smaller or farther away than it is. However, scientists do not yet understand completely why the moon seems to shrink as it rises in the sky.

    I remember the first time I got on a horse. When I was a little boy aged two, my mom agreed to let me take a short ride and that was it! From then on, I drove my parents crazy begging for a horse.

    When I was four, I had mutism, in which children stop speaking in certain social situations. I went days, weeks, months without a sound at school. At most, I might quietly whisper to a friend. I suffered silently through school until I was ten when a psychologist had an idea. He asked me what I wanted more than anything else in the world. He explained I was going to be given an opportunity to work for that. And I was permitted to whisper the answer in my mother's ear, “A horse.”

    I was to get a horse, but I had to finish many weekly tasks. I had to answer the phone five times per week, something I had never done before. I had to say one word to my teacher at school and the list went on. For a child with mutism, saying one word to someone can be like climbing Mount Qomolangma. I did everything that was asked of me and the day came. His name was Sequoia, whom I fell in love with immediately. When I was with Sequoia, I forgot all about my problems and felt strong and secure.

    I am participating in society these days. My horse and I made it through a master's degree. I feel I owe my life to the horse and I try to give it back to him every day. He has given me the best gift I could ever imagine, my life.

    Each year there is an increasing number of cars on roads and streets as millions of new cars and trucks are produced. One out of every six Americans works at putting together the parts of cars, driving trucks, building roads or filling cars and trucks with gas. Americans won't live without cars!

    Most Americans would find it hard to think what life would look like without cars. However, some have realized the serious problems of the air pollution that is caused by the car.

    The polluted air becomes poisonous and dangerous to health.

    One way to get rid of the polluted air is to build a car that does not pollute. That's what several of the large car factories have been trying to do. But to build a clean car is easier said than done. Progress in this field has been slow.

    Another way is to take the place of the car engine by something else. Inventors are now working on steam cars as well as electric cars. Many makers believe that it will take years to develop a practical model that pleases man.

    To prevent the world from being polluted by cars, we'll have to make some changes in the way many of us live. Americans, for example, have to cut down on the number of their total cars. They are encouraged to travel and go to work by bicycle. Bicycling is thought to help keep the air clean.

    But this change does not come easily. A large number of workers may find themselves without jobs if a car factory closes down. Thus the problem of air pollution would become less important than that of unemployment.

    Although cars have led us to a better life, they have also brought us new problems.

    We arrived at the hospital to find Dad was very weak, but his smile was as sure as ever. It was another attack of pneumonia (肺炎). My husband and I stayed with him for the weekend but had to return to our jobs on Monday. Local relatives would help Dad get home from the hospital and look after him. But I longed to be able to let him know that we cared too, even when we weren't with him.

    Then I remembered a family tradition when our children were small. When leaving their grandparents' home after a visit, each child would write a love note to their grandparents. They hid notes in the cereal (麦片) box, under a hairbrush, next to the phone or even in the microwave oven (微波炉). For days, their grandparents would smile as they discovered these signs of our love.

    So as I tidied Dad's kitchen and made up a bed for him downstairs in the living room, I wrote some notes. Some were practical, “Dad, I put the food in the fridge so it wouldn't spoil.” Some expressed my love, “Dad, I hope you will sleep well in your new bed.” Most notes were downstairs where he would stay for several weeks until he recovered strength, but one note I hid upstairs under his pillow, “Dad, if you have found this note, you must be feeling better. We are so glad!”

    Just like his medicines strengthened him physically, these “emotional vitamins” would improve his spiritual health. Several weeks later, in one of our regular phone calls, I asked Dad how he was doing. He said, “Pretty good. I just found your note under my pillow upstairs!”

    When he was 22, Rob Stewart traveled the world for four years. He wanted to call attention to the mistreatment of sharks. His 2007 film, Sharkwater, documents the cruel practice of removing sharks' fins (鳍) for money and leaving the animals to die. In his latest documentary, Revolution, Stewart takes on an even bigger challenge: climate change.

    The Canadian filmmaker says that climate change has harmed people and places everywhere: "It is stronger than any government or organization. If we educate people, they will make better decisions about protecting natural resources. "

    According to a recent report on climate change, "The atmosphere and ocean have warmed, the amounts of snow and ice have reduced, and sea levels have risen." These developments are endangering crops, wildlife, fish, and even people.

    Stewart says that the consequences of climate change will be irreversible unless people take action, especially young people."It's up to kids to be the moral compass (道德指南) of society," he believes, "and say, 'Guys, this is not right.'"

    Many kids took action after seeing Sharkwater. Elementary school students in the Northern Mariana Islands, for example, got their local government to ban the sale of shark fins.

    Felix Finkbeiner, 17, of Germany is also part of the "revolution" to save the planet. In 2007, Felix started a youth group called Plant-for-the-Planet, whose motto is "Stop Talking. Start Planting." The group raises money to plant trees. So far, Plant-for-the-Planet has planted nearly 200 trees around the world. "Future generations are the ones who will be suffering the most from inaction (无作 )," Felix says. His goal is to plant millions of additional trees.

    "When we started four years ago," Felix tells Stewart in Revolution, "we thought we had to save the polar bear. We thought we had to save the environment. But soon after, we found out that it's about our future, that we have to save our own future."

Grizzly bears,which may grow to about 2.5 m long and weigh over 400 kg,occupy a conflicted corner of the American psyche—we revere(敬畏) them even as they give us frightening dreams.Ask the tourists from around the world that flood into Yellowstone National Park what they most hope to see,and their answer is often the same:a grizzly bear.

"Grizzly bears are re-occupying large areas of their former range,"says bear biologist Chris Servheen.As grizzly bears expand their range into places where they haven't been seen in a century or more,they're increasingly being sighted by humans.

The western half of the U.S.was full of grizzlies when Europeans came,with a rough number of 50,000 or more living alongside Native Americans.By the early 1970s,after centuries of cruel and continuous hunting by settlers,600 to 800 grizzlies remained on a mere 2 percent of their former range in the Northern Rockies.In 1975,grizzlies were listed under the Endangered Species Act.

Today,there are about 2,000 or more grizzly bears in the U.S.Their recovery has been so successful that the U.S.Fish and Wildlife Service has twice attempted to de-list grizzlies,which would loosen legal protections and allow them to be hunted.Both efforts were overturned due to lawsuits from conservation groups.For now,grizzlies remain listed.

Obviously,if precautions(预防) aren't taken,grizzlies can become troublesome,sometimes killing farm animals or walking through yards in search of food.If people remove food and attractants from their yards and campsites,grizzlies will typically pass by without trouble.Putting electric fencing around chicken houses and other farm animal quarters is also highly effective at getting grizzlies away."Our hope is to have a clean,attractant-free place where bears can pass through without learning bad habits,"says James Jonkel,longtime biologist who manages bears in and around Missoula.