The African elephant, the largest land animal remaining on earth , is of great importance to African ecosystem(生态系统). Unlike other animals, the African elephant is to a great extent the builder of its environment. As a big plant-eater, it largely shapes the forest-and-savanna(大草原)surroundings in which it lives, therefore setting the terms of existence for millions of other animals that live in its habitat(栖息地).

    It is the elephant's great desire for food that makes it a disturber of the environment and an important builder of its habitat. In its continuous search for the 300 pounds of plants it must have every day, it kills small trees and underbushes, and pulls branches off big trees. This results in numerous open spaces in both deep tropical forests and in the woodlands that cover part of the African savannas. In these open spaces are numerous plants in various stages of growth that attract a variety of other plant-eaters.

    Take the rain forests for example. In their natural state, the spreading branches overhead shut out sunlight and prevent the growth of plants on the forest floor. By pulling down trees and eating plants, elephants make open spaces, allowing new plants to grow on the forest floor. In such situations, the forests become suitable for large hoofed plant-eaters to move around and for small plant-eaters to get their food as well.

    What worries scientists now is that the African elephant has become an endangered species. If the elephant disappears, scientists say, many other animals will also disappear from vast areas of forest and savanna, greatly changing and worsening the whole ecosystem.

    Whether you are entering the job market for the first time or you are already at work, you have to know the various fields where you can work and the types of jobs available per field. Now it is time that you gained basic knowledge about ten common fields of work and some types of jobs in that field. Here they are:

    Technology Jobs

    The technology field is always growing very fast, so job growth in the field is also constantly booming. Here, you are always in the cutting-edge. However, you always have to update your skills when you are working in technology. Engineering and IT graduates are people who primarily do work related to technology.

    Education Jobs

    Here is a field which allows you to share your knowledge with others. You need subject-matter knowledge and teaching skills to be in this field. Most of all, you need plenty of hearts. While the everyday life of teachers may be tiring, education is one of the most fulfilling (令人满意的) fields to enter. You may need some certifications, though.

    Healthcare Jobs

    Healthcare professions enable you to use a great knowledge base of the human body and of latest health advances so you can save lives, provide comfort, cure illness, and maintain people's health. Work here is often done in hospitals and private clinics.

    Science and Mathematics

    Discovering new knowledge is the primary task of scientists and mathematicians. Training here takes a long time and goes beyond getting a bachelor's degree. However, the work will be fulfilling, especially that you may be at the edges of revolutionary discoveries. You can also use any experience and research skills acquired in either field to work in regular employment settings.

    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 bet that on cold winter days, many of you love to stay in your warm home and, every now and then, come out into the kitchen for a snack. Unfortunately, plenty of small insects like to do the same thing! Winter is the time when small insects enter your house without an invitation. The season can be difficult for such creatures. In winter the air is cold, the ground is hard and many trees have no leaves. So small insects do what they have to do to survive.

    Monarch butterflies head south to warmer climates. Ants crowd in deep underground colonies and eat food they have been storing all year. Many insects go into a deep sleep called diapauses. There're different kinds of diapauses, but all are similar to hibernation, a time when bigger animals become inactive in the cold. Insects go into an inactive period, too, but it often isn't when the temperature drops.

    They rely on more dependable signals in the environment. For example, many insects can tell how much sunlight there's each day. They use that to tell themselves when to shut down. Insects are cold-blooded, meaning that their inside temperature is the same as the outside. They can't move much when it gets below 40 degrees Fahrenheit. So they search for any warm place.

    They're looking for protection. These guys have been doing this for 300 million years, so they don't really know they're coming into your house. The home is a recent event in terms of their evolutionary (进化的) behavior. They enter through tiny cracks or come in unnoticed on your clothes or shoes. Remember that they may be entering your homes for warmth and food, but they don't care about humans.

    I left university with a good degree in English Literature, but no sense of what I wanted to do. Over the next six years, __________ just trying to earn an income. I tried journalism, but I didn't think I was any good, then finance, which I hated. Finally, I got a job as a rights assistant at a famous publisher. I loved working with books, although the job that I did was dull.

    I had enough savings to take a year off work, and I decided to try to satisfy a deep-down wish to write a novel. Attending a Novel Writing MA course gave me the structure I needed to write my first 55,000 words.

    It takes confidence to make a new start — there's a dark period in-between where you're neither one thing nor the other. You're out for dinner and people ask what you do, and you're too ashamed to say, "Well, I'm writing a novel, but I'm not quite sure if I'm going to get there." My confidence dived. Believing my novel could not be published.

    I put it aside.

    Then I met an agent(代理商)who said I should send my novel out to agents. So, I did and, to my surprise, got some wonderful feedback. I felt a little hope that I might actually become a published writer and, after signing with an agent, I finished the second half of the novel.

The next problem was finding a publisher. After two-and-a-half years of no income, just waiting and wondering, a publisher offered me a book deal — that publisher turned out to be the one I once worked for.

    It feels like an unbelievable stroke of luck — of fate, really. When you set out to do something different, there's no end in sight, so to find myself in a position where I now have my own name on a contract of the publisher — to be a published writer — is unbelievably rewarding.

A 293-million-mile journey of the NASA Perseverance rover (探测器) to Mars: ended successfully on February 18, 2021, with a picture-perfect landing inside the Jezero Crater. The car-sized, six-wheeled rover, nicknamed Percy is the US space agency's biggest and most advanced explorer to date. Its primary mission is to search for signs of ancient microbial (微生物的) life on Mars.

Landing on Mars is extremely tricky. The Red Planet's gravitational pull causes approaching spacecraft to go faster to high speeds, while its thin atmosphere-just 1 percent that of Earth's-does little to help slow it down as it approaches the surface.

The scientists had to reduce Percy's 12,000 mph speed to a safe landing speed of less than five mph-in just six and a half minutes. The target entry angle also had to be a precise 12 degrees-any steeper, and the spacecraft would burn up; any flatter, and it would get lost in space. It is no wonder that the final approach is often referred to as the "seven minutes of terror. "

Upon attaining a manageable speed, Percy briefly flew over the Martian surface to seek out the perfect landing spot. Its complex map-reading system rapidly scanned the area and matched it with maps in its database to find the best location.

The NASA scientists will spend the next two months testing Percy's scientific instruments. Once ready, the rover will begin to carry out its mission.

"Perseverance is the smartest robot ever made, but confirming that microbial life once existed carries an unusually large burden of proof," said Lori Glaze, director of NASA's Planetary Science Division. "While we'll learn a lot with the great instruments we have aboard the rover, it may very well require the far more well-equipped laboratories and delicate instruments back here on Earth to tell us whether our samples (样本) carry evidence that Mars once harbored life. "