铝及铝合金表面脱脂，一般可采用有机溶剂、表面活性剂或弱碱性清洗剂来进行。( )

铬(Cr)属于重金属元素，含铬的废水和废渣在排放前必须经过相应处理并达到相关的安全标准。

(1)铬的原子序数为24，铬位于周期表中第___周期第___族。

(2)铬元素常以Cr₂O₇^2-的形式存在于酸性废水中，常用硫酸亚铁将其还原为Cr³⁺，再用沉淀法分离除去。已知：当1×10^-6mol．L^-1≤c(OH -)<1×10^-4mol．L^-1时，则发生的反应的离子方程式为Cr³⁺ +3OH^-=Cr(OH)₃↓；当c(OH ^-)≥1×10^-4 mol．L^-1时，则Cr( OH)₃溶于碱生成CrO₂^-。

①在酸性条件下，硫酸亚铁还原Cr₂O₇^2-的离子方程式为___。

②向硫酸铬[Cr₂(SO₄)₃]溶液中加入过量的氢氧化钠浓溶液，反应的离子方程式为___

③常温下，采用沉淀法除去废水中的Cr³⁺，应控制的pH范围是___。

④下列关于铬及其化合物的说法中正确的是___。

A．K₂Cr₂O₇是一种常用的强氧化剂

B．NaCrO2溶液与氯化铝溶液混合有沉淀生成

C．酸性K₂Cr₂O₇溶液可用于检验司机是否酒后驾车

D．金属铬硬度大，耐腐蚀，是常用的镀层金属

Most "unassertive" people are not confident and take no for an answer much too easily. There is a growing awareness in our society that this tendency (1) the rights of large numbers of people. For example, in recent years there has been an upsurge in (2) and pressure groups. This is a (3) as there will always be a need for such organizations to (4) individuals and minorities in a competitive society. The danger is that we (5) for our rights and lose the art of asserting ourselves. It is better for (6) with other people if you can learn (7) for yourself.
Now, we have to learn to ignore some of the (8) that may be ringing in our unconscious minds, such as: "If you ask once more, I’ll flatten you", and " (9) ".
The main technique that we use in (10) to practice the art of persistence is called Broken Record. (11) we hear one sentence over and over again until we reach screaming pitch and (12) .
Broken Record is the skill of being able to repeat over and over again, (13) , what it is you want or need, until the other person gives in or (14) .
Now, this technique is extremely useful for dealing with situations where your rights are clearly (15) , or coping with situations where you are likely to be diverted by clever, (16) .
The beauty of using Broken Record is that you (17) because you know exactly what you are going to say, however (18) the other person tries to be.
As with most assertive techniques, it must be used appropriately. It is (19) and is not designed to foster deep, interesting conversations and friendships with people! It is primarily of use in situations where (20) .

在站台前有甲、乙两列原来静止的火车，突然，坐在乙车上的乘客发现，站台和甲车都在以相同的速度运动，那么，他选择的参照物是( )。

A．甲车

B．乙车

C．站台

D．无法判断

障碍性乘客应尽可能地靠近出口座位附近就座。

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