题干

金属钛(Ti)是一种具有许多优良性能的较为昂贵的金属,钛和钛合金被认为是21世纪的重要金属材料.某化学兴趣小组在实验室探究Ti、Mg、Cu的活泼性顺序,他们在相同温度下,取大小相同的三种金属薄片,分别投入等体积等浓度足量稀盐酸中,观察现象如下:

金属

Ti

Mg

Cu

金属表面现象

放出气泡速度缓慢

放出气泡速度快

无变化

下列有关三种金属的说法正确的是(   )

A:三种金属的活泼性由强到弱的顺序是:Ti、Mg、Cu

B:若Ti粉中混有Mg,提纯Ti时可用稀盐酸除去Mg

C:用Ti从CuSO4溶液中置换出Cu是工业制取Cu的很好途径

D:温度、金属表面积、盐酸浓度等因素都会影响反应速率

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D

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    Getting rid of dirt(灰尘), in the opinion of most people, is a good thing. However, there is nothing fixed about attitudes to dirt.

    In the early 16th century, people thought that dirt on the skin was a way to block out disease, as medical opinion had it that washing off dirt with hot water could open up the skin and let illnesses in. A particular danger was thought to lie in public baths. By 1538, the French king bad closed the bath houses in his kingdom. So did the king of England in 1546. Thus it began a long time when the rich and the poor in Europe lived with dirt in a friendly way. Henry IV, King of France, was famously dirty. Upon learning that a nobleman had taken bath, the king ordered that, to avoid the attack of disease, the nobleman should not go out.

    Though the belief in the merit of dirt was long-lived, dirt has no longer been regarded as a nice neighbor ever since the 18th century. Scientically speaking, cleaning away dirt is good to health. Clean water supply and hand washing are practical means of preventing disease. Yet, it seems that standards of cleanliness have moved beyond science since World War ll. Advertisements repeatedly sell the idea: clothes need to be whiter than white, cloths ever softer, surfaces to shine. Has the hate for dirt, however, gone too far?

    Attitudes to dirt still differ hugely nowadays. Many first-time parents nervously try to warm(警告)their children of touching dirt, which might be responsible for the spread of disease. On the contrary, Mary Ruebush, an American immunologist(免疫学家), encourages children to play in the dirt to build up a strong immune system. And the latter position is gaining some ground.