1. Concentration is essential if you want to do a good job.
    如果你想把事情做好，专心是必要的。

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2. What is the concentration of salt in sea water?
    海水中盐的含量是多少？

3. This thesis will need all your concentration.
    这篇论文需要全神贯注才能读懂。

4. There is a concentration of people in big cities.
    大城市人口集中。

1. concentration：con; 专注力

1. 全神贯注;专心;专注
    Concentration on something involves giving all your attention to it.

    e.g. Neal kept interrupting, breaking my concentration...
           尼尔不停地打断我，使得我无法集中注意力。
    e.g. We lacked concentration and it cost us the goal and the game.
           我们注意力不够集中，结果丢了球，输了比赛。

2. 集中;汇集
    A concentration of something is a large amount of it or large numbers of it in a small area.

    e.g. The area has one of the world''s greatest concentrations of wildlife...
           这个地区是世界上野生动物最为密集的区域之一。
    e.g. There''s been too much concentration of power in the hands of central authorities.
           权力一直过多地集中在中央机构手中。

3. 浓度
    The concentration of a substance is the proportion of essential ingredients or substances in it.

    e.g. pH is a measure of the concentration of free hydrogen atoms in a solution...
           pH值是测试溶液中自由氢原子浓度的单位。
    e.g. The latest data showed that global ozone concentrations had dropped several per cent over the last decade.
           最新数据显示，过去10年来全球臭氧的浓度降低了几个百分点。

1. strengthening the concentration (as of a solute in a mixture) by removing diluting material

2. bringing together military forces

3. great and constant diligence and attention

    Synonym: assiduityassiduousness

4. the strength of a solution
    number of molecules of a substance in a given volume

5. the spatial property of being crowded together

    Synonym: densitydensenesstightnesscompactness

6. complete attention
    intense mental effort

    Synonym: engrossmentabsorptionimmersion

7. increase in density