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钢铁工业是国家工业的基础．2006年我国粗钢产量突破4亿吨，居世界首位．某中学社会实践活动小组利用假期对当地钢铁厂进行了调研，对从矿石开始到钢铁产出的工艺流程有了全面的感性认识．请您对社会实践活动小组感兴趣的问题进行计算：

将6.72g铁矿石样品投入适量的盐酸中（充分反应），过滤，然后在滤液中加过量的NaOH 溶液，充分反应后，过滤、洗涤、灼烧得4.80g Fe2O3．现以该铁矿石为原料炼铁，若生产过程中铁元素损失4%，计算每生产1.00t生铁（含铁96%），至少需要这种铁矿石多少吨？（保留两位小数）

答案

氧化铁中铁的质量为4.80 g×

112
160
=3.36g，

即根据铁元素守恒可知，6.72g铁矿石中铁的质量为3.36g，

设需要这种铁矿石x吨，

由铁矿石质量～铁的质量的关系式，则

   矿石～生铁 

6.72g    3.36g

xt×（1-4%）   1.00t×96%

6.62g
x吨×(1-4%)
=
3.36g
1.00t×96%
，

解得x=2.00t，

答：需要这种铁矿石2.00吨．

单项选择题

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 (1) to a large extent on the relationship of the color (2) other colors (3) simultaneously. It is not (4) in its relation to the direct stimulus which (5) it. On the other hand, the properties of surfaces that give (6) to color do not seem to change greatly under a wide variety of illumination color, usually (but not always) looking much the same in artificial light as in daylight. Both of these effects seem to be (7) in large part to the mechanism of color (8) .

When the eye is (9) to a colored area, there is an immediate readjustment of the (10) of the eye to color in and around the area (11) . This readjustment does not promptly affect the color seen but usually does affect the next area to which the (12) is shifted. The longer the time of viewing, the higher the (13) , and the larger the area, the greater the effect will be (14) its persistence in the (15) viewing situation. As indicated by the work of Wright and Schouten, it appears that, at (16) for a first approximation, full adaptation takes place over (17) time if the adapting source is moderately bright and the eye has been in (18) darkness just previously. Also, (19) 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 (20) over the whole eye.

8（）

A.assimilation

B.admission

C.regulation

D.adaptation
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单项选择题

已有定义：int x=3，y=4，z=5，则表达式!(x+y)+z-1&&y+x/2的值是

A．6

B．0

C．2

D．1
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