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The only solid pieces of scientific truth about which I feel totally confident is that we are profoundly ignorant about nature. Indeed, I regard this as the major discovery of the past hundred years of biology. It would have amazed the brightest minds of the 18th century Enlightenment to be told by any of us how little we know and how bewildering seems the way ahead. It is this sudden confrontation with the depth’ and scope of ignorance that represents the most significant contribution of the 20th century science to the human intellect. In earlier times, we either pretended to understand how things worked or ignored the problem, or simply made up stories to fill the gaps. Now that we have begun exploring in earnest, we are getting glimpses of how huge the questions are, and how far from being answered. It is not so bad being ignorant if you are totally ignorant; the hard thing is knowing in some detail the reality of ignorance, the worst spots and here and there the not-so-bad spots.
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(每题的备选项中，只有1个最符合题意) 某工程公司中标承包一城市道路施工项目，道路总长15km，路面采用沥青混凝土。该路地处平原地区，路基横断面的填方3～6m高的路堤为主，借方量大，借方的含石量40%～60%。地表层以黏土为主，地表层土厚7～8cm，土的天然含水量为40%～52%，地表无常年积水，孔隙比为1.2～1.32，属典型的软地基。 重力密度是指土的重力与其体积之比，一般为( )。
Americans smoke six thousand million cigarettes every year, that is, every person smokes about 4,195 cigarettes a year in the country of 18 years of age or more. It has been calculated that 51% of American men smoke while 34% of American women do so.Since 1939, scientific studies have shown that smoking does great harm to one’s health and it will shorten one’s life.Cigarette smoking is believed, by most research workers in the field, a very important cause in the development of the cancer of the lungs and the cancer of the throat and is believed to have much to do with some other kinds of cancers. Cigarette smokers suffer from the illness of the heart more often than those who don’t smoke. But strange, yet true, women are thought to be less affected, because when women smoke, they usually don’t breathe in the smoke so deeply. Most of doctors and researchers say, "Give up smoking. If you don’t smoke--don’t start!"Filters (过滤嘴) are required now to make smoking a bit safer, but they can only reduce, not get rid of, its poison.But there are still a number of doctors and research workers who are less sure of the effect of cigarette smoking on health. They believe that the cancers of the lungs, the throat and so on may also be caused by air pollution, or chemical poison that is now being used by farmers in large quantities to destroy plant pests and small animals. It is believed by many that the cancers of the lungs and throat are caused()by smoking.
W: Come in and sit down.M: Thank you. Here I’ve got a small present for you for Christmas.W: How nice of you! Let’s open it right now. Oh, how lovely it is!M: This small basket will be just right for candy and some other little things.W: Where did you get itM: It’s from China. Two months ago, I went to China with my parents and I bought it for you in Beijing, the capital of China.W: From China Thank you so much. No wonder it’s so lovely. China’s famous for its handicrafts. Let me see what it is made of.M: It’s woven of bamboo.W: Really How skillfully it’s done! I’ll get it right here. Everybody can see it when coming in.M: I’m very glad you like it. Where does this conversation take place()
As one works with color in a practical or experimental way, one is impressed by two apparently unrelated facts. Color as seen is a mobile changeable thing depending to a large extent on the relationship of the color to other colors seen simultaneously. It is not fixed in its relation to the direct stimulus which creates it. On the other hand, the properties of surfaces that give rise to color do not seem to change greatly under a wide variety of illumination colors, usually (but not always) looking much the same in artificial light as in daylight. Both of these effects seem to be due in large part to the mechanism of color adaptation mentioned earlier. When the eye is fixed on a colored area, there is an immediate readjustment of the sensitivity of the eye to color in and around the area viewed. This readjustment does not immediately affect the color seen but usually does affect the next area to which the gaze is shifted. The longer the time of viewing, the higher the intensity, and the larger the area, the greater the effect will be in terms of its persistence in the succeeding viewing situation. As indicated by the work of Wright and Shouted, it appears that, at least for a first approximation, full adaptation takes place over a very brief time if the adapting source is moderately bright and the eye has been in relative darkness just previously. As the stimulus is allowed to act, however, the effect becomes more persistent in the sense that it takes the eye longer to regain its sensitivity to lower intensities. The net result is that, if the eye is so exposed and then the gaze is transferred to an area of lower intensity, the loss of sensitivity produced by the first area will still be present and appear as an "afterimage" superimposed on the second. The effect not only is present over the actual area causing the "local adaptation" but also spreads with decreasing strength to adjoining areas of the eye to produce "lateral adaptation." Also, because of the persistence of the effect if the eye is shifted around from one object to another, all of which are at similar brightness or have similar colors, the adaptation will tend to become uniform over the whole eye. The present selection has apparently been preceded by some explanation of ______.
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