Facebook is an Internet-based social network site that lets people get in touch with family and friends and reach out to people with common interests around the world, all through computer. It is very popular, with more than 900 million users. If Facebook were a country, it would have about three times the population of the United States.

    Documents filed with US. financial regulators say Facebook has hundreds of millions of active users who send billions of messages each day and upload 250 million photographs on their personal pages. Facebook users have registered 100 billion “friends.”

    On Facebook, “Friending” someone means you add the person to your list of people you can communicate with directly, which often allows the person to see more information about you than you share with the general public.

    Facebook was started by Mark Zuckerberg and other students at Harvard University in 2004, and has grown at an amazingly fast pace.

    Facebook makes money when advertisers pay to get access to hundreds of millions of Facebook users. Advertisers can often direct their messages to the people most interested in their products because Facebook computers keep track of information that users place on their pages. For example, a person interested in diving, planning a wedding, looking for work, or suffering from diabetes(糖尿病) may see advertisements related to those topics.

    Facebook has become so much a part of the culture of the United States and other nations that it has been the subject of a Hollywood movie. It is a key marketing tool for many businesses, and its users' content has been used as evidence in some divorce or criminal cases.

根据短文内容，选择最佳答案，并将选定答案的字母标号填在题前括号内。

    Life-Changing Science Discoveries

    Here's a look at some discoveries that have changed the world. It's impossible to rank their importance, so they're listed in the order they were discovered

Micro-organism

    Before French chemist Louis Pasteur began experimenting with bacteria in the 1860s, people did not know what caused disease. He not only discovered that disease came from micro-organisms, but also realized that bacteria could be killed by heat and disinfectant(消毒剂). This idea caused doctors to wash their hands and disinfect their instruments, which has saved millions of lives.

Penicillin

    Antibiotics are powerful drugs that kill dangerous bacteria in our bodies that make us sick. In 1928, British Alexander Fleming discovered the first antibiotic, penicillin, which he grew in his lab. Without antibiotics, infections like strep throat could be deadly

DNA

    On February 28, 1853, James Watson of the United States and Francis Crick of England made one of the greatest scientific discoveries in history. The two scientists found the structure of DNA. Our genes are made of DNA and determine how things like what color hair and eye we'll have. In 1962, they were awarded the Nobel Prize for this work . The discovery has helped doctors understand diseases and may someday prevent some illnesses like heart disease and cancer.

X-rays

    Wilhelm Roentgen, a German physicist, discovered X-rays in 1895. X-rays go right through some substances, like flesh and wood, but are stopped by others, such as bones and lead. This allows them to be used to see broken bones or explosives inside suitcases, which makes them useful for doctors and security officers. For this discovery, Roentgen was awarded the first-ever Nobel Prize in Physics in 1901.

    If you could have one superpower, what would it be?

    Dreaming about whether you would want to read minds, see through walls, or have superhuman strength may sound silly, but it actually gets to the heart of what really matters in your life.

    Every day in our work, we are inspired by the people we meet doing extraordinary things to improve the world.

    They have a different kind of superpower that all of us possess: the power to make a difference in the lives of others.

    We're not saying that everyone needs to contribute their lives to the poor. Your lives are busy enough doing homework, playing sports, making friends, seeking after your dreams. But we do think that you can live a more powerful life when you devote some of your time and energy to something much larger than yourself. Find an issue you are interested in and learn more. Volunteer or, if you can, contribute a little money to a cause. Whatever you do, don't be a bystander. Get involved. You may have the opportunity to make your biggest difference when you're older. But why not start now?

    Our own experience working together on health, development, and energy the last twenty years has been one of the most rewarding parts of our lives. It has changed who we are and continues to fuel our optimism about how much the lives of the poorest people will improve in the years ahead.

    For many people, the Transformers movies are the greatest Hollywood blockbusters (大片). And among the Transformers themselves, the yellow Autobot named Bumblebee is certainly the favorite. He may be one of the smallest and weakest of the alien machines, but he is always loyal to his friends and shows great bravery in battle.

    In the new film, Bumblebee is found in a junkyard (废车场) and is full of honeybees. He always finds himself in awkward (尴尬的) situations, but people like his cute and naive looks. In addition to his blue eyes, Bumblebee's body language and movements are adorable. At one point, he sits with his legs straight out, with his huge feet making him look like a 5-year old trying on his dad's shoes.

    Bumblcbee is the Transformer who has the greatest affinity (亲和力) with humans. He starts journey with Watson, who is at a loss about her future and wants a friend. As a result of their adventure together. Watson grows up and starts to work toward her life goal of becoming a musician. As for Bumblebee, as we know, is a robot from outer space, he now has a better understanding of his task to protect the Earth. Every adventure has a beginning, as the movie poster puts it. More importantly, every adventure needs a good partner. The considerate, positive and warm Bumblebee is definitely a good choice according to US actress I Hailee Stcinfeld, who plays Watson in the film.

    A new study has found the amount of antibiotics(抗生素)given to farm animals is expected to increase by two-thirds over the next 15 years. Researchers are linking the growing dependence on the drugs to the increasing need for meat, milk and eggs. However, the drugs could quicken the development of antibiotic-resistant infections(感染). Such infections are already a major public, health concern in the United States.

    The World Health Organization notes when people stop living in poverty(贫困), the first thing they want to do is eat better, rather than earn more money. For most people, that means their diet should contain more meat. With the rapid development of Asia, people there are eating nearly four times as much meat, milk and other milk products as they did 50 year ago.

    To meet the need, farmers have put many animals into smaller spaces. As the animals are crowded together, the easiest way to deal with some of the problems of crowding is to give them antibiotics. It's clear that antibiotics help animals stay healthy in a crowded environment and grow faster. But bacteria can develop resistance to the drugs gradually.

    Nowadays, doctors find antibiotics that once worked against the infections no longer work. The bacteria have learned ways to fight against the drugs. The heavy use of antibiotics in animals is responsible for the growth of antibiotic resistance worldwide. In the United States, at least two million people get drug-resistant infections each year and at least 23,000 die from an infection.

    Europe has banned the use of antibiotics to increase animal growth. And the United States is hoping to persuade farmers to stop using antibiotics for that purpose.

    A new study suggests that patients with breast cancer who take additional vitamins during chemotherapy(化疗) treatment may face increased risks.

    Researchers said the use of dietary supplements(补充剂) that increase levels of antioxidants, iron, vitamin B12 and omega-3 fatty acids appeared to lower the effectiveness of chemotherapy. Researchers reported their findings in the Journal of Clinical Oncology.

    Christine Ambrosone is the head of cancer prevention and control at the Roswell Park Comprehensive Cancer Center in Buffalo, New York. She said, "From this study and others in the literature, it seems that it may not be wise to take supplements during chemotherapy."

    "It's thought that antioxidants might interfere with the ability of chemotherapy to kill cancer cells," Ambrosone said.

    Some doctors have been advising patients for a number of years not to take antioxidants during chemotherapy. "But there was no strong empirical data for that recommendation," Ambrosone said.

    So, Ambrosone and other researchers decided to study whether supplement use might affect chemotherapy's effectiveness. They looked for evidence in an earlier study on diet, exercise, lifestyle and cancer results.

    In the earlier research, people who took part were asked about their use of supplements at the beginning of and during treatment, and about their lifestyle, diet and exercise. The researchers studied 1,134 patients who filled out the surveys and followed them for a median of six years.

    The researchers searched for possibilities that might increase the risk of the disease reappearing or of death. They found that patients who took any supplements at the beginning of and during chemotherapy were 41 percent more likely to have their breast cancer return than those who did not. In addition, the supplement takers were 40 percent more likely to die later on compared to patients using no supplements. The supplements included vitamin A, C and E. Those taking vitamin B12 and iron supplements were at greater risk of cancer returning, the researchers said.