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问题 选择题

下列除去杂质的方法正确的是

 物质杂质试剂主要操作
ANaHCO3固体Na2CO3固体/加热
BSiO2Fe2O3盐酸过滤
CKBr溶液Br2KOH溶液分液
DCl2HCl饱和碳酸钠溶液洗气
 

答案

答案：B

题目分析：A、加热只会除去碳酸氢钠，错误；B、氧化铁与盐酸反应，而二氧化硅不反应，正确；C、使用KOH溶液会引入其他杂质，错误；D、氯气也与碳酸钠溶液反应，同时会产生杂质二氧化碳气体，错误，答案选B。

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.

19（）

A.regardless

B.despite

C.exclusive

D.because
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单项选择题

对β受体具有兴奋作用的药物是（）.

A．肾上腺素

B．盐酸普萘洛尔

C．盐酸哌唑嗪

D．盐酸异丙肾上腺素

E．酒石酸去甲肾上腺素
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