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明朝
明朝统治中国276年，被人们描绘成人类历史上治理有序、社会稳定的最伟大的时代之一。这一时期，手工业的发展促进了市场经济和城市化。大量商品，包括酒和丝绸，都在市场销售。同时，还进口许多外国商品，如时钟和烟草。北京、南京、扬州、苏州这样的大商业中心相继形成。也是在明代，由郑和率领的船队曾到印度洋进行了七次大规模探险航行。还值得一提的是，中国文学的四大经典名著中有三部写于明朝。
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宋朝
宋朝始于960年，一直延续到1279年。这一时期，中国经济大幅增长，成为世界上最先进的经济体，科学、技术、哲学和数学蓬勃发展。宋代中国是世界历史上首先发行纸币的国家。宋朝还最早使用火药并发明了活字(movable-type)印刷。人口增长迅速，越来越多的人住进城市，那里有热闹的娱乐场所。社会生活多种多样，人们聚集在一起观看和交易珍贵艺术品。宋朝的政府体制在当时也是先进的。政府官员均通过竞争性考试选拔任用。
Batteries Built by Viruses What do chicken pox, the common cold, the flu, and AIDS have in common？ They're all disease caused by viruses, tiny microorganisms that can pass from person to person. It's no wonder that when most people think about viruses, finding ways to steer clear of viruses is what's on people's minds. Not everyone runs from the tiny disease carriers, though. In Cambridge, Massachusetts,scientists have discovered that some viruses can be helpful in an unusual way. They are putting viruses to work, teaching them to build some of the world's smallest rechargeable batteries. Viruses and batteries may seem like an unusual pair, but they're not so strange for engineer Angela Belcher, who first came up with5 the idea. At the Massachusetts Institute of Technology (MIT) in Cambridge, she and her collaborators bring together different areas of science in new ways. In the case of the virus-built batteries, the scientists combine what they know about biology, technology and production techniques. Belcher's team includes Paula Hammond, who helps put together the tiny batteries, and Yet-Ming Chiang, an expert on how to store energy in the form of a battery. "We're working on things we traditionally don't associate with nature," says Hammond. Many batteries are already pretty small. You can hold A, C and D batteries6 in your hand. The coin-like batteries that power watches are often smaller than a penny. However, every year, new electronic devices like personal music players or cell phones get smaller than the year before. As these devices shrink, ordinary bakeries won't be small enough to fit inside. The ideal battery will store a lot of energy in a small package. Right now, Belcher's model battery, a metallic disk completely built by viruses, looks like a regular watch battery. But inside, its components are very small-so tiny you can only see them with a powerful microscope. How small are these battery parts？ To get some idea of the size, pluck one hair from your head. Place your hair on a piece of white paper and try to see how wide your hair is-pretty thin, right？ Although the width of each person's hair is a bit different, you could probably fit about 10 of these virus-built battery parts, side to side, across one hair. These microbatteries may change the way we look at viruses？ According to the first paragraph people try to
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