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问题 选择题

恒容密闭容器中进行的可逆反应2NO2⇌2NO+O2，达到平衡状态的是（　　）

①单位时间内生成a mol O2的同时生成2a mol NO2

②单位时间内生成a mol O2的同时生成2a mol NO

③混合气体的颜色不再改变

④混合气体的密度不再改变的状态

⑤混合气体的平均相对分子质量不再改变的状态．

A．①③⑤

B．②④⑤

C．①③④

D．①②③④⑤

答案

此题列出了判断可逆反应是否达到平衡状态的各种可能情况，应从平衡状态的两个重要特征上判断（1）v（正）=v（逆），（2）混合物中各组成成分的百分含量不变．①符合特征（1）；②表示的都是正反应方向；③NO2是红棕色气体，颜色不变时说明NO2的浓度保持不变，符合特征（2）；④中若是恒容条件，则ρ始终不变；若恒压条件，则ρ随反应而变；⑤也说明符合特征（2）．故①③⑤能说明是否达到平衡状态．

故选A．

完形填空

语法填空(共10小题；每小题1. 5分，满分15分)

阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空，并将答案填写在答卷标号为3l-40的相应位置上。

A man, now old, went overseas 40 years ago. On his     31      ( depart ), the girl he loved gave him as a souvenir a heart-shaped knot made of knitting wool. He     32     ( hang ) it on his belt ever since.

Several years later he got married and had children. As time went by his sweetheart’s      __33___ ( look ) became dimmer and dimmer like a landscape picture    34     ( fade ) away gradually, and his homeland only appeared in his dreams. In the evening of his life he often looked at the knot and sighed.

One day his grandson caught sight of the knot and insisted on getting hold of it as a toy. The boy fondled ( 抚弄 ) and tried to unfold it. At last he did    35     trick and got it loose and open.

When it      36       ( spread ) out it resumed ( 重获 ) its form as a long thread, a very simple wool thread.      37    by the skillful hands of a beloved girl could the thread be knitted into such a complicated knot. Devoted love made so many simple things complex in the world.

Thus the old man was awoken to get a truth. Most of the grievances ( 抱怨 ), bitterness and hatred in life actually result from very small matters.      38      one is mindful of them, they become mental knots. But if one sees     39      the knot, it remains a simple thread or line, no matter     40      shape it assumes.
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单项选择题

两种声音的声强级差1分贝，则它们的强度之比为（）。

A．0.0126

B．0.126

C．1.26

D．12.6
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