Harvard researchers have created a tough, low-cost, biodegradable (可生物降解的) material inspired by insects' hard outer shells. The material's inventors say it has a number of possible uses and someday could provide a more environmentally friendly alternative to plastic. The material, made from shrimp ('虾) shells and proteins produced from silk, is called "shrilk." It is thin, clear, flexible and strong.

    A major benefit of the material is its biodegradability. Plastic's toughness and flexibility represented a revolution in materials science during the 1950s and '60s. Decades later, however, plastic's very durability (耐用性) is raising questions about how appropriate it is for one-time products such as plastic bags, or short-lived consumer goods, used in the home for a few years and then cast into a landfill where they will degrade for centuries. What is the point of making something that lasts 1,000 years?

    Shrilk not only will degrade in a landfill, but its basic components are used as fertilizer(肥料), and so will enrich the soil.

    Shrilk has great potential, the inventors said. Materials from which it is made are plentiful in nature, found in everything ranging from shrimp shells, insect bodies to living plants. That makes shrilk low cost, and its mass production possible should it be used for products demanding a lot of material.

Work on shrilk is continuing in the lab. The inventors said the material becomes flexible when wet, so they're exploring ways to use it in wet environments. They're also developing simpler production processes, which could be used for non-medical products, like for computer cases and other products inside the home. They're even exploring combining it with other materials, like carbon fibers, to give it new properties.

请列举出分别能体现北京是我国的政治中心和文化中心的代表性建筑物。

①羊群   撒在   雪白的   草原   大   的   一望无际   上

②菊花   盛开   秋天   着   千姿百态   的   公园里

③可以   鸟   研究   空气   资料   污染   为   可贵   的   提供

    Sunday is more like Monday than it used to be. Places of business that used to keep daytime “business hours” are now open late into the night. And on the Internet, the hour of the day and the day of the week have become irrelevant. A half century ago in the United states, most people experienced strong and precise dividing lines between days of rest and days of work, school time and summer time. Today the dividing lines are still there, but they seem not clear.
    The law in almost all states used to require stores to close on Sunday; in most, it no longer does. It used to keep the schools open in all seasons except summer, in most, it still does. And whether the work week should strengthen its legal（法律的）limits, or whether it should become more changeable, is often debated（争论）. How should we, as a society, organize our time? Should we go even further in relaxing the dividing lines of time until we live in a world in which every minute is much like every other?
    These are not easy questions even to ask. Part of the difficulty is that we seldom recognize the “law of time” even when we meet it face to face. We know as children that we have to go to  school a certain number of hours, a certain number of days, a certain number of years – but unless we meet the truant officer（学监）, we may well think that we should go to school because of social custom and parents’ requirement rather than to the law. As adults we know “extra pay for overtime working” very well, but less familiar with the fact that what constitutes（构成）“overtime” is a matter of legal thing. When we turn the clock forward to start daylight – saving time, have we ever thought to ourselves: “Here is the law in action”? As we shall see, there is a lot of law that has great influence on how organize and use time: compulsory education law, overtime law, and daylight-saving law – as well as law about Sunday closing, holidays, being late to work, time zones, and so on. Once we begin to look for it, we will have no trouble finding a law of time to examine and assess.